.
A Caveat
Undergravel filters have not been widely tested as a filter in the aquaculture industry, The limited testing done on gravel filters for aquaculture was “all over the map” due to the very high loading of commercial operations. So one is left with common sense and low load testing by the author as the only sources of information in the analysis below.
Another Caveat
Yes, the price of aquarium gravel is very high. But all indications from everyone, including some recent experiences of my own, say that an undergravel filter does best with 3/16ths aquarium gravel. Everything else, including sand, Black Diamond abrasives, oil absorbent, large pea gravel, foam, etc. has large downsides. So I recommend just biting the bullet and buying “natural” cream, tan and dark brown mixed aquarium gravel. It will pay for itself in the long run.
The Myths
Ahhhh yes the myths live on.
Aquarium equipment manufacturers and fish stores who want to sell expensive canister filters (ah, the profit motive at work!) have invented a whole host of negative points about under-gravel filters. None of these points withstands scientific scrutiny. Under gravel filters are still one of the best forms of filtration out there.
Note the brightest, most honest fish keeper in the business, Cory of Aquarium Co-op, recommends under gravel filters. Most shops do not promote them because it is a onetime low profit purchase with no return business. Air operated under gravels have no moving parts that need replacing. I have been using some under-gravel filters for some thirty years and they are still working well. If one can get five years out of most canisters and HOBs, you are doing well. External filters frequently leak but under gravels cannot leak. Canisters frequently spring leaks.
Note that if you clean under gravels frequently, they are a pain in the butt and do not work. If you just leave them alone, they are a great, inexpensive filter with a huge bioload capacity. Put a powerhead on them and they become even better biofilters. “Old technology” like under gravels have only been superseded by our need for shiny new things and expensive “must-haves” that we do not really need. I had them in sixteen tanks and loved them.
Under-gravel Filters and Biofiltration
Under-gravel filters are great for biofiltration (the media volume is second only to sumps) and crystal-clear water AS LONG AS YOU DON’T CLEAN THEM BUT EVERY FEW YEARS. The brown “gunk” in the gravel isn’t fish feces or “accumulated nitrates”, it is a “brown gunk” (my term for a type of biofilm) filled with beneficial bacteria and many other beneficial organisms which are very good for your aquarium (“beneficial bacteria ain’t pretty”).
From the Poret Foam Supplier (Swiss Tropicals):
“The brown filter sludge in a filter is for the most part alive and not simply waste. Removing this mud does more harm than good. The purpose of the filter media is not to filter out particles from the water as is often assumed. The media serves as the habitat for a vast array of microorganisms that include bacteria, archaea, worms, ciliates, flagellates, and many others. These microorganisms live in a community that is based on biofilms. The biofilms are created by bacteria that secret extracellular polymeric substance (EPS), which is often called “slime”. The community forms a bioreactor that processes the waste and turns it into food and energy for its members, and ultimately into organic or inorganic products that are then used by plants, evaporate, or removed by water changes. It takes a considerable amount of time to establish this “filter community”; consequently, it is very important not to disturb it unless absolutely necessary.”
This is a probably the most intelligent statement any aquarium products distributor has ever made.
By the verb “clean” above, we mean stirring up the gravel and creating a brown soup which is then removed. We do not mean cleaning under the plates or dismantling the whole thing. There is NEVER a need to do that. The gravel of under-gravel filters will never go hypoxic so bacterial toxins are not a worry if the gravel is stirred.
If under gravels are frequently cleaned (and the term “cleaned” includes “deep vacuuming”) they do not work. But if one uses cheap food that is loaded with fillers one can clog up even an under-gravel. So if your food is under 40% protein, one can vigorously stir up an under gravel once a year or so and then remove 75% to 95% of the brown water. The brown water left behind will reseed the under gravel very rapidly. And the fish won’t be harmed by the brown gunk in the water column.
Now there is a caveat. ANY filter, including an undergravel, can be overloaded. If one over feeds a heavily stocked aquarium with a food that has low protein levels then you can create a cesspool. And NO filter, including an undergravel, will clean up a cesspool.
We’ve used under-gravel filters in typically five to fifteen very heavily stocked tanks (which included large digging cichlids) for fifty years. Every two years or so I stir up the gravel and create a brown soup. I then do a 90% water change with frequent stirring of the water to keep everything in suspension.
The under-gravel filters have given us: no ammonia spikes, no build-up under the plates, no “exposed plates”, no “nitrate factory”, no “clogging”, no “disease reservoirs” and no “anaerobic dead areas” (even under décor). And we typically had very heavily stocked cichlid aquariums.
One decided advantage of undergravel filters is that the downward water flow oxidizes and removes feces and mulm above the gravel very rapidly. This makes for a much healthier and much more attractive aquarium. You just will not see feces and mulm floating above the gravel for long if there is an undergravel filter.
And then there is the mechanical problems of hang-on-back and canister filters. We’ve had lots of leaks, seized pumps and noisy pumps with hang-on back and canister filters. Sometimes they have leaked out of the box. And they only last two to five years in my experience. We’ve had several floors damaged by leaks. That is an expensive failure. We’ve had some under-gravel filters for thirty years (maybe even much longer!) with no problems what’s-so-ever and no replacements of anything.
How an Under-gravel Filter Works
Under gravel filters consist of a plastic grate or “filter plate” which lies under small gravel in the aquarium. The thickness of the gravel should be one to two inches, This plate allows water to flow freely under the gravel. Water is lifted up a “lift tube” by a flow of air. This flow then draws water down through the gravel. The gravel then acts as an excellent biological filter.
.
Operation of the undergravel filter
To move the water in an under-gravel filter you use an air pump which moves air into the aquarium through air tubes. This air pump will blow bubbles from an air stone at the bottom of the lift tubes and the bubbles will lift water up the lift tube and into the aquarium. This then draws water down through the gravel.
And the type of air lift used is important. Many under-gravel filters use a simple hole to produce very large bubbles that rise in the air lift tube. The large bubbles are very noisy and throw spray in all directions when they surface. Modify any such filter to use an air stone.
The many small bubbles of an air stone lift much more water than the large bubbles of the hole. So under-gravel filters that use airstones are much better than holed under-gravel filters. The ideal air bubble size is about one tenth of an inch.
One can alternatively add a pump called a “powerhead” directly to the top of the lift tube. There is no need for an air pump, air stones or air tubes with the powerhead. This makes the cost of the two systems quite similar. I like the powerheads as they are decidedly quieter than air stones and air pumps. Also powerheads move more water than air stones and gives somewhat better biofiltration.
I use small four to five watt powerheads and I aim the duckbill defector at the surface to maximize the “choppy waves”. This “breaking the surface tension” gives very good aeration.
This diagram shows how to use a powerhead with a under gravel filter. If there are two lift tubes use two powerheads.
Another idea which came from Cory of Aquarium Co-op is to put the suction end of a canister on the top of the undergravel filter tube. This would seem to be a great idea until you realize a leaking canister will remove ALL the water in the aquarium and kill ALL the fish. Whoops.
In order to use a canister in line with an undergravel filter one must add a hole halfway up the intake tube. This way one can only drain half the water before the siphon is broken. But the size of the hole becomes critical. Too big and you short circuit the undergravel. Too small and you don’t break the siphon. So all-in-all it is an arrangement I don’t recommend.
Comparing Under-gravel filters to other filters gives the following:
# of 3″ Fish* refers to the number of fish for which this filter can give very clear healthy water. Ammonia oxidation is twenty times easier and these numbers can be multiplied by twenty if the only consideration is ammonia.
Note that under-gravel filters need to be purchased on the internet now-a-days due to the determined efforts of the profit minded filter manufacturers (Petco still stocks them). Also note that it is very feasible to buy an under-gravel filter for say a 30 gallon aquarium and install it on ANY tank larger than 30 gallons.
Note also that for some inexplicable reason the price of aquarium gravel has skyrocketed lately. Some of it is selling for $1 a pound. At three pounds of gravel for every gallon of tank that is $150 worth of gravel for a fifty gallon tank. But note that aquarium gravel is pretty standard as a substrate. Sand is cheaper but has some serious drawbacks.
Opposition to Under-gravel Filters
Many well meaning but ill-informed commentators on social media pan under-gravel filters and very few hobbyists use them as a result. The problem is that the panning originated in the marketing departments of manufacturers and suppliers interested in selling expensive canister filters. When local fish stores realized they made more money on expensive canister filters sales then inexpensive under-gravel filters they joined in the chorus. Isn’t the profit motive wonderful?
And then social media got involved. The well meaning but ill-informed commentators on social media did the standard thing of parroting what they had heard from other posts. What the parrots failed to realize is that those posts were put there by canister manufacturers. We have documented this form of social media “influencing” by manufacturers of expensive aquarium goods.
The chief complaint we see about under-gravel filters is that it is “antiquated technology” or “old school”. Since when is something “bad” simply because it has been around for a long time? Is the wheel antiquated?
When we have pressed the various well meaning but ill-informed commentators on social media who criticize our use of under-gravel filters on why under-gravel filters are bad, the best they can come up with is that they are “nitrate factories”.
Then we point out that all good filters are nitrate factories. Indeed, the function of all biofiltration is to oxidize ammonia to nitrate and that one gram of ammonia nitrogen is converted to one gram of nitrate nitrogen regardless of where or how it is done (this is a basic law of physics called “conservation of matter”). They then fail to come back 100% of the time. They have no comeback possible.
Another common complaint is that the brown gunk that builds up in the gravel is very bad “dirty” stuff that is very detrimental to the aquarium. This idea that brown gunk is detrimental is the single biggest myth promulgated in the hobby. We go into that in great depth in the undergravel in depth link below (and in many other articles throughout this website). The brown gunk is beneficial bacteria and other organisms which reduce the pollution in the aquarium, not add to it.
Another common complaint is twofold, that under-gravel filters need to be cleaned frequently of brown gunk and that they don’t work. These two complaints are just sadly self-fulfilling prophecy . Under-gravel filters work far better if they aren’t cleaned. So the folks who are cleaning under-gravel filters regularly are only insuring that their under-gravel filters don’t work as well as they should.
There are some aquarium hobbyists who are interested in delving deep into the science and the calculations behind all aspects of the hobby. For those who are so inclined the following is pertinent:
8.5.1. Under-gravel Filters in Depth
DIY Undergravel Filters
We have designed a DIY undergravel filter for those with a DIY bent. It is not cheap but some want such a design:
8.5.2. DIY Undergravel Filter
Bottom of the Tank Matten Under Gravel Filter
Another interesting type of under gravel filter is placing a piece of charcoal colored foam across the bottom of the aquarium over under gravel filter plates. We discuss this in this article:
8.7.7. Bottom of Tank Matten Filter
.
Return to Filters Menu
.
Tank Start Guide Website
The chapters shown below or on the right side in maroon lead to close to 400 articles on all aspects of keeping a freshwater aquarium. These articles have NO links to profit making sites and are thus unbiased in their recommendations, unlike all the for-profit sites you will find with Google. Bookmark and browse!
.
Hi Dave I have undergravel filter in my tank. I have two giant turtles with two tin foil barbs that are just as large as the turtles. I know that the no. 1 rule of UG filters is you don’t clean them but I feel that this is based on fish-only tanks. I wonder if it’s applied to heavy-load tanks as well? I clean the gravel once a month because if I don’t, the brown gunk piles up and covers the entire substrate to the point that it’s no longer visible. It took several months by the way.
In reply to Shana … ANY filter, including an undergravel, can be overloaded. You are overloading an undergravel and will need to clean it frequently.
I really appreciate all this info! I am thinking about getting back into the hobby and always loved my UGFs. Really enjoying the aguascaping movement and excited to set up a zero maintenance aquarium in the 20-30 gal range. Has anyone used aqua soil in bags above a UGF w/ powerhead? My plan is to install the grates, add a 2″ (thicker?) layer of gravel, put 2-4 mesh bags with aqua soil on the gravel (to build up hills on each end of the tank) and then cover the aqua soil bags with gravel. The thought being the aqua soil will help the plants get started while I increase the number of fish over time. My concern is mainly that the agua soil will come out of the bag and migrate into the filter grates causing the system to clog.
In reply to Brandon …. Your concerns are well founded. Aquasoils break down into a clay like sediment which will clog the UGF plates. And the water flow through the aquasoil will put all the nutrients into the water column very rapidly. I wouldn’t recommend aquasoil with an UGF.
Hello Sir, The Mbuna I got they are moving the gravel and I have undergravel filter. I know you have told not to get crushed coral but this is only what I could find with the Guy I dealt for all other things. What shall I do? They haven’t reached the bottom as I have about 1.5 inch gravel from the front going up to 03 inches to the back. Will they dig it up fully or if they do will it affect my Aquarium? They remain in one corner of the tank and are very skittish, just got them a week ago. Thank you.
In reply to Amit …..Yes they will expose the plates on an undergravel. It turns into a game. They expose the plates, you cover them back up. I used to play it on a daily basis with my mbuna. It doesn’t seem to affect the operation of the filter at all. So do not worry about it.
I have a HOB filter now, was about to get a sponge filter. I had an under gravel years ago before I gave up the hobby for motherhood. I now have a 30 gallon, and want to go back to the UG filter. Is the hassle of uprooting the tank worth it, or just go with the sponge?
You have several options. For small aquariums like a 20 gallon I like the Sunsun HW-603B External Canister Filter ($40). It has 80 cubic inches foam which makes a great biological filter if you only very lightly clean it once every four to eight months (ignore the profit minded directions which say to replace the foam). Also I like under gravel filters ($20). If you clean under-gravel frequently, they are a pain in the butt and do not work well. If you just leave them alone, they are a great inexpensive filter. Matten filters are also good inexpensive options as are good old sponge filters. Personally I would go ahead and add a powerhead operated undergravel but that’s just what I do.
Dear Dave,
Thanks for the great website!! I’ve got a background in microbiology, and between your info and father fish, I became quite enamoured with the idea of running a dirted tank with a living ecosystem containing as complete a food chain as one can maintain in a small tank full of ravenous predators. In order to get the bacteria as diverse as possible, I decided to go with 75% enriched substrate + sandcap, 25% UGF. Normally everybody says you cant have a UGF in a dirted tank, but I simply put it in a plastic tray and buried it carefully such that sand cant get into it in any significant amount.
Got to say, my tank water was extremely clear after only three days, despite having a significant bacterial bloom before that. I’ve got ten little zebra danios and ten chilli rasbora, and they are all doing quite fine by the looks of it. We are looking to add a few denizens (shrimp and a bristlenose) soon, now that some algae is starting to show and going after your “if the water clears, the filter is ready for more fish” metric. I’ll just make sure to deworm for planaria before hand (and will have to carefully culture and add detritus and blackworms later).
Dave, I’ve really enjoyed your website and now I’m sold on trying a UGF for my first tank setup in 30 years. Thanks for the info you’ve already posted! Even after reading the comments, I have several questions.
I have a tall 56-gallon tank with an oddball 30×18 footprint. I was able to find several kits with the same modular, 7.5×14.5cm grid-plate design that slots together and gives reasonably complete coverage. It seems best to use both lift tubes that came with my plates, and small powerheads on each of them. Is there a “gph” rating that would be best to keep under? Something like a combined 3x to 5x the tank volume in rated turnover, or whatever? I don’t need to recreate a hillstream level of current inside the tank (saving that for my patio pond). But I would rather go with pumps than air stones.
I’d also like to keep some plants that don’t have “Java” in the name, would it make sense to keep the powerheads’ output lower in the water column to minimize surface agitation and CO2 off-gassing? (I assume that would also necessitate relatively light fish stocking levels.)
Bagged aquarium gravel is basically highway robbery these days. I’ve been checking local landscaping suppliers for a crushed stone product that’s aquarium-gravel sized and keep striking out. You mention “sand” being an issue with UGFs on this page but don’t really elaborate on that. Could I use medium (12-40) Black Diamond blasting grit as the substrate over them? I already have some washed, since this was going to be a Walstad-type dirted tank originally. I also have pool filter sand, which I understand is more tightly screened to keep clogging fines out and ensure good flow.
I tested some BD with my UGF grill plates and it seems I’d at least need to use some weed barrier fabric to keep it from passing right through. A gentle sift let every single grain fall through the plates.
I’d really appreciate any light you could shed on these questions, even if it’s to tell me I’m going about this all wrong.
In reply to Kyle …..I just use the smallest powerheads I can buy as one doesn’t need a lot of flow with an undergravel filter. Output low in the tank if you wanted planted (and yes, few fish). As for the gravel I would bite the bullet and get the expensive 3 to 6 mm aquarium gravel from the store. It is just the best stuff for an undergravel filter.
Note that you are describing a high tech planted tank with low fish loading. A small canister might well be a better choice than an undergravel, given the price of the gravel.
hi dave can i use basalt gravel on aquael separating the coarse fraction above 3mm for Undergravel filters. It is not mentioned anywhere about basalt as a media
Basalt gravel will work just fine
what percentage of the tank bottom must be covered by the filter plates?
In reply to Steve ….. Just maximize it. There is no magic number.
Thank you for this excellent evidence based blog, it has been a real help! I enjoyed the nerdy parts.
May I ask, would it be possible/helpful to connect an undergravel filter to a sump filter (as in, in series with the lift tube from the undergravel plate connected to the sump K1 reservoir?)
In reply to SY …… Part of the sump set-up is balancing the flows so everything works correctly. This is difficult to do with an undergravel as part of the equation. So all my setups which had both had the undergravels on separate loops
I was ready on the web site of a fish seller that UGF are not recommended for Corydoras. They say that they can lose their barbels if kept in poor conditions (dirty substrate).
What’s your experience with those fish.
Yan …. The detritus in an undergravel filter won’t affect the barbels of corydoras. I’ve had probably hundreds of corydoras over the years with UGFs and never had any problems.
For an undergravel filter, what powerhead do you recommend? Ive never used them before so I know nothing about what would be a reliable one. I’ve seen that Fluval has some, aquaclear has some, marine land and topfin, as well as names I don’t recognize. I was looking at a pennplax UGF on Amazon and it has a 1inch diameter lift tube and I want to make sure a powerhead would fit properly. Thanks for your help
In reply to Cody ….. ALL powerheads are made in China and are equally unreliable. I simply buy the cheapest ones available on Amazon. Usually they fit a one inch lift tube quite well but adding some meat to the powerhead with some duct tape is also quite easy.
Thanks Dave. Now as far as substrate goes I use gravel but was thinking of adding some Fluval stratum substrate under the gravel for my plants. Will that work with an UGF or will that clog it up?
In reply to Cody… Fluval stratum substrate will not plug up an undergravel filter. But note that the product is a scam and doesn’t help plants at all.
The Fluval stratum is a volcanic soil that is in a gravel like form and its to help plants grow and have more nutrients than just gravel. I don’t want to clog up the UGF if I use it so if it’s going to do that I can just stick to my gravel.
Thanks Dave, I think unless there’s mulm corys will be ok.
Hiya from downunder
Love your resource. It has become a life saver to me to cut through the bullshit. I’m trying to transition toward undergravel filters because I like the simplicity and the silence. Unfortunately I really don’t like the look of gravel. I am trying to think of options and I am looking at the matten type modification you mentioned and/or sponge down the track. But I have 2 questions for now
1. Could I put down a bed of gravel as per your instructions and cover it at the front top and sides with a layer of slate crushed to a smaller gravel type size 5-10mm or use the 4-5cm chips I have without crushing them?
2. Can I use slate crushed to gravel size alone on top of the undergravel filter? Or is it too smooth for biomedia.
3. I notice you mentioned using 4-5 watt powerheads. I have easy access to those Kmart filters and they attach very nicely to the uplift tubes but they are only 200L/hour about 2.5 watt. Would they be suitable or would you recommend having 2 of these pumps instead of the one 4-5watt powerhead you recommend using? Do you have a litre per hour recommendation for the powerheads, it seems 4-5x the tank volume might be unnecessary for an ugf from reading your site.
Many thanks in advance.
Kieran
In reply to Kieran …..
1, I don’t think you like the “engineered rough tile” look you’ll get with a gravel slate mix
2, Crushed slate is just a form of crushed gravel and will work just fine for an UGF
3, Flow is no where near as important as myth would suggest. 1-2x the volume is fine, including for UGFs
I used an UGF many years with crystal clear water. Loved it.
Now….my 1 year old 20 gal planted aquarium has been cloudy for the last month or so. The uptake tubes get coated and look like they are bringing up the brown gunk from underneath the UGF. (My previous aquarium never did that.)
The airflow is very good and the gravel is very clean. I do a 20% water change every 2 weeks.
Could my airstones be either too far down in the tubes….or not far enough?
Any ideas?
Thanks.
Hello, do you have any opinions on tunning a powerhead on reverse flow? I have seen it mentioned around the web and it allows for a sponge in the inlet that should help with mechanical filtration.
What about a pull push ( one side of the tank with a reverse flow and the other one with a normal flow) configuration to generate a slow current below the substrate?
Thank you.
In reply to Felipe …. Reversing the flow on an undergravel is pretty well a wash. You lose the ability to aerate the water exiting the powerhead. Note any undergravel filter is an excellent mechanical filter and needs no help. And any “push-pull” designs will simply short circuit any undergravel design and render it inoperative.
Hi Dave thank you for the reply.
If UGFs are good mechanical filters why did you award them 0 points in mechanical filtration in the table in section 8.1 ?
Thank you.
In reply to Felipe …… I put together 8.1 before I realized just how good UGF are for mechanical filtration
Several years ago, I used to have a 29 gallon tank with an UGF and my fish did fine. Unfortunately, I was one of those who cleaned it entirely by breaking it down, including cleaning the gravel each time. I’m surprised none of my fish died which included two angel fish, a betta, a clown loach, and some dwarf frogs, after dumping them back in with less than 50% of their water that I saved each time. About 10 years ago, I got back into the fish hobby again and again, used UGF. I thought the brown sludge was too much to clean so I ended up using hanging filters. It’s been six years since I changed to HOB filters and still struggle with keeping the nitrate down, even with changing my water every week to ten days. After reading this article, it was an eye-opener to realize I didn’t have to remove the brown sludge with my UGF, but to instead, embrace it. I would like to give it another try with my 55 gallon tank that I currently use, but I’m wondering how often would I need to do a water change? I usually change out 25% with my HOB filters (two), so would I need to change out the water just as often? And how much should I remove?
In reply to Shari ……. Do a fifty percent water change when nitrates hit 80 ppm. Note that the nitrate test is often misread. Avoid looking at the darkness of the tube. Instead look only at the color. Orange is 40 ppm while 80 ppm is red orange.
Hey Dave! Thanks so much for your resource. It’s truly been a lifesaver. I didn’t know how much I didn’t know until I found your site and I’m so grateful you’ve taken the time to compile this information for free.
I want to do a planted tank with an under-gravel filter after hearing your feedback. For this, I was thinking of using gravel topped with aqua soil. What do you think? Or should I do it the other way around—aqua soil then gravel? No aqua soil at all and only gravel?
Also, I know you don’t typically link externally as you don’t have a profit motive, but can you point me to your favorite under-gravel filter readily available on something like Amazon?
Thank you so much in advance! Hope you’re enjoying your holidays!
In reply to Kayla ….. Gravel only. Forget the aqua soil. And I just buy the cheapest UGF that fits the tank
Hello Dave,
I am starting up a 55 gallon tank and I had purchased two canisters that provide lots of biomedia. The canisters were a great price from a major manufacturer and have used them before. But now sitting over a crawlspace with wood flooring, I am a bit concerned by the potential for leaks.
I am considering the following options, trying to balance filtration capacity with leak risk:
1. Dual canisters without a UGF
2. Dual canisters with a UGF, with the canister inflow/outflow removed when away from the house
3. UGF only
In all cases with the canisters, I’d be putting them in the cabinet with a bin and leak detector.
I could always sell the new canisters but was leaning toward option 2 for the over-filtration and mitigated risk.
Thoughts welcome and thanks!
In reply to Frank ….. Your option two is the best balance. And a single powerhead will do it for the UGF.
Oh and related to the below, if doing the UGF in a 36×18 footprint, would one powerhead be enough if I have the two canisters? The UGF dimensions would likely be 33ish x 11
I’m new to this hobby, and i have a week old aquarium with undergravel filter with canister filter attached to it.
I’m using probably 95% pot scrubbers as a media and 5% polishing filter media. but I’m having a DOC problem, there’s many particles in the water, and plant matter. DOC wasn’t a problem when i my canister filter uses lily pipe as an intake. i don’t know what i did wrong, or things gonna be better overtime.
In reply to anonymous …… Yes, it is time related. It will probably be one or two months before the undergravel gets to doing its job. Just have patience.
love the site. I set up a 20g tank with an undergravel thanks to your information. It’s doing great and super low maintenance. Crystal clear water. As I think about my next tank I am thinking 100-125 gallons. I think it will probably be mostly a low tech planted tank with many nano fish. Think aquascape. But perhaps I would change my mind if I ever feel like my water is quality enough for large fish like discus. I’ve been going back and forth between trying to figure out building a fluidized sump versus just doing undergravel with powerheads again. I don’t think my bio load will be huge unless I decide on discus or other big fish. If I do undergravel only, is more gravel generally better or is there a point of diminishing returns? I am thinking it would start at 1 or 2” and then slope up as high as 4” of gravel. Is that increasing my biological media or preventing flow?
Thanks!
Jon
In reply to Jonathan …… add the heavy dose of gravel. It is virtually impossible to have too much gravel in any undergravel filter. The ONLY time I have seen problems with flow through an undergravel was when sand was added to the gravel.
Hi Dave,
1. Using UGF w/air stones, is it ok to have varying thickness of substrate, i.e. a slope from front to back or perhaps a few mounded areas of gravel or will that diminish the effectiveness of the UGF?
2. My 40B size is 36w x 18d x 16t. Using UGF w/airstones, are two uplift tubes (one in each back corner) sufficient or should there be more uplift tubes and/or a different placement of the tubes?
Hi Dave, in regards to my previous questions, I re-read everything again and see that you addressed that varying depth of gravel is ok. Also in a 60 gallon breeder you recommended adding a 3rd uplift tube in the middle. So my only remaining question is whether for a 40-g breeder you also recommend a 3rd uplift tube or will two (one in each corner) be sufficient. Thanks so much.
In reply to Sandi …… Two will be enough.
Put a 1inch layer of filter floss over the under gravel filter plate and place about 2/3inches of gravel on top.. This method has been tried and we’ll proven.
In reply to Ed ……….. cichlids will produce tons of loose floss if you mix cichlids with this method of undergravel filter.
Currently setting up a UGF in a 75 gallon, what’s the optimal size of powerhead(s)? 2 big 70s? or 3-4 smaller 20-30s??
In reply to Jimmy …….. The larger is better IF THE FISH CAN TAKE THE CURRENT. For instance, African Cichlids can take the current, discus can’t take the current.
Hi again Dave, I’m using an UGF w/ airstones in a 40 breeder tank, gravel substrate thickness varies 1.5-3″. 10hp variable air pump. I performed a dark start fisless/plantless cycle following your tips, and added plants and started adding small fish 2 weeks ago. Feeding lightly high protein food.. The water has remained crystal clear (except for tannins). Looking underneath the tank I was surprised to see brown gunk under the plates already. Is this normal or does it indicate there is a problem with my operation? I’m wondering if I’m running the pump too high and pulling detritus through the gravel faster than can be consumed by the BB. And do I need to siphon this out and recalibrate. Thanks.
Sandi ……. That brown gunk is very GOOD for the tank and indicates you are doing things 100% correctly. Just leave it be and all will be just fine.
Using an undergravel filter, how much do you estimate the flow of a powerhead gets reduced, if it even does, compared to the specifications of the manufacturer, assuming they are 100% accurate? for example, if I use an Aquaclear Powerhead 30, in Europe it would have 660 l/h of maximum flow, that would probably be at the same height in the output without trying to push water upwards with a tube in the output or something like that. I guess what I’m trying to understand is if the fact that water has to go through the gravel and also the pump has to maybe exert more effort into sucking water from being tightly connected to a tube and the water coming from like 30cm lower than where the pump sits at, reduces the flow in any meaningful way.
I ask this because I want to reduce the noise to the maximum possible, especially the low humming noise, also reduce the power consumption too. I have a 240L tank, around 60 gallon, would probably be around 200L of effective water when excluding glass thickness, gravel and water height level. So aiming for a minimum of 2x turnover, would I get at least around 400 l/h of flow from this 66 l/h pump?
In reply to anon ……….. Forget flow and turnover as indicative of filter efficiency. They are not indicative of filter efficiency. Simply use small powerheads to reduce noise and power consumption.
In reply to anon ……….. Forget flow and turnover as indicative of filter efficiency. They are not indicative of filter efficiency. Simply use small powerheads to reduce noise and power consumption.
660 l/h pump sorry.
Hi Dave, thank you again for the massive amount of work it took to put together this website and for your continuing to answer our questions. Here’s a few more.
1. Re using UGF with fish that prefer minimal to no flow – I turned down my air pump to be easier on my tetras and a soon-to-arrive gouramis. I also aimed the corner outflows toward the sides of the tank at about 45 degrees. I do still have lots of air bubbles breaking at the surface/turbulence (currently ‘course’ airstones & I just ordered ‘fine’) and I’m not sure the flow will suit the gouramis. How do I know how far I can turn down the pump to accommodate fish needs and still get the turnover needed for good filtration?
2. Re water changes. It’s been 3 weeks since I did a max water change + added the first round of fish (32 very small fish in a 40b) in a planted tank. Since then I’ve only topped off the tank about ever other day. I appear to have clear water, healthy fish, growing plants, no visible algae, 0 ammonia, 0 nitrite, essentially undetectable nitrate since I also added floating plants. I have very hard well water. My GH & KH have always been off-the-chart high, PH has increased from high to off-the-chart high. I’m wondering when & if I need to do a water change. There are those on the ‘net that say just topping off hard water will eventually lead to too high concentration of minerals and then I’ll have ‘old tank syndrome’ where old fish have acclimated but new fish won’t be able to adjust. I’ve also heard that that’s total hogwash.
In reply to Sandi ………. 1, Tetras and gouramis will adjust to more flow than most folks give them credit for it. But there is no formula or “rule”. Just whatever you feel comfortable with.
2, You are doing just fine, obviously. And topping off with hard water will not cause “old tank” syndrome. Too high a pH will affect plants though. Most plants don’t like high hardness and pH. If you start having plant problems consider more water changes or an RO system
One thing that is not clear to me is, what determines the ideal number of uplift tubes?
For example, in a 60 gallon tank with only one uplift tube at the center, will the water go through all the gravel? would two uplift tubes with each pump having less flow rate be better in terms of reaching all the gravel?
Another question, is the flow cumulative? so is one uplift tube with one pump with 250 GPH roughly the same, as far as flow efficiency, as two uplift tubes with two pumps with 125 GPH each? because if each uplift tube gets more access to a certain gravel area than the other, that gravel area could have a low enough flow, right? then maybe it wouldn’t be fast enough as far as outcompeting bacteria in the water column?
In reply to anon …………… I’ve always spread out the load with multiple tubes and low flow powerheads. But I have no firm data on which to base that ideal. Likewise I think you are accurate as far as the sizing but I have no firm data to back that up.
Anon, regarding pump noise, I wanted to share with you that once I upsized my air pump, the pump was much quieter because presumably it doesn’t have to work as hard. I can hardly hear it.
Dave,
I have a bunch of 35 gallon cubes I am setting up for pairs for breeding. I found UG filter plates that are square and can be clicked together. The tank dimensions on the inside bottom are about 20″. I am planning to set up nine of the UG filter plates connected. Each plate side is 5.9 inches and they are lifted a bit off the tank bottom. The size would leave a bit of space around the perimeter, about an inch. Does that work ok?
The uplift tubes are around .87 inches in diameter…Is there a power head you would recommend that would fit that and what kind of gph or wattage do I need for a 35g cube tank for freshwater angel fish pairs and plants? How do I attach the uplift tube to the plates? Can I use two uplift tubes, one in each back corner?
Sorry for all the questions…. I am autistic and adhd and feeling a bit overwhelmed with all the information so I thought I could maybe just ask directly. A link to the undergravel squares I bought are below. The uplift tube link is below that one.
https://www.walmart.com/ip/OUNONA-Aquarium-Bottom-Filter-Grid-Tray-20pcs-Tank-Divider-Tray-Isolation-Board-Under-Gravel-Enhancer-System-Aquatic-Accessory/15489022698
https://www.amazon.com/dp/B0C5Z2YRGH?ref=ppx_yo2ov_dt_b_fed_asin_title
Thank you so much!
Dawn
In reply to Dawn ……. Scrap the two items you have outlined. They don’t appear to have compatible connections. Instead buy anyone of several kits where the lift tubes come with the plates. And I just buy small 400 liter per hour powerheads to go with those setups.
Dave – your website is amazing! As a bioprocess engineer, everything makes sense and really admire your ability to change your opinions based on new data.
Based on your guidance, I set up a UGF in my 5g Fluval tank last spring and also loaded the original internal filter chamber with 40 ppi foam filter – and now I have a heavily filtered aquarium that is able to support 20+ one inch fish (tetras & danios) with crystal clear water!
For my next 40g tank project, I plan to use 30 ppi sponge foam in lieu of gravel – though I might add a 1/2″ thin layer of gravel on top of the sponge for aesthetics. I plan to also install an internal overflow chamber (will drill holes in the bottom) and connect to a fluidized media sump.
I would like to avoid having lift tubes – mainly to minimize surface area for algae growth and also for an uncluttered aesthetic look. So I’ll run 1/4″ HDPE airlines in the plenum UNDER the filter plates and have multiple bubbling stones (one in each corner) poking out of the sponge foam layer. I’ll also have a 1/2″ pipe connected directly to an intank recirculation pump located in the overflow chamber and that should pull the water through the UGF and pumped back into the tank. The bottom of the overflow chamber will be completely sealed from rest of the tank including the UGF, except for the 1/2″ pipe connection.
Do you think that pulling the water through the 1/2″ pipe at one end of the tank would be sufficient for filtering through 500 sq in. of the bottom filter? Or would you suggest that I install the lift tubes + powerheads instead?
In reply to ChiliG35 ……… I’ve never tried anything like what you describe so I don’t know if it will work or not. Sorry.
No worries Dave.
I’ll install lift tube holders just in case – that way I won’t have to redo the entire bottom if I don’t get enough flow through the bottom matten filter bed. I have silicone caps that fit the lift tube holders (and I’ll drill out the caps for the air tubing connecting to the air stones).
I’ll let you know how this goes in a few months!
Hi Dave,
Question about plants and UGF. Following your advice I set up a 40g w/UGF and it’s humming along nicely with minimal maintenance, moderate stocking and a variety of live plants. I’m still experimenting finding which plants will do well in my hard well water & high pH. Most recent adds are amazon swords and so far look promising. I have however been following an interesting thread on Aquarium Co-op forum re UGF and a recent commenter stated “… I had to remove an Amazon sword that was growing out the top of/totally filled a 25G tank. Its roots had almost completely filled the area under the UGF.” Yikes. Should I pull the swords? This is a heavily planted and hardscaped tank and I loathe the thought of my UGF becoming compromised and needing to break it apart someday or add other filtration. What do you think?
Btw if you’re interested in the thread started by Cory here’s the link https://forum.aquariumcoop.com/topic/50615-undergravel-filter-rabbit-hole/
In reply to Sandi…….. That is a risk with any heavily planted UGF tank. What I’m not sure about is the “so what”. If the space under an UGF becomes filled with roots , will the flow or the filtration be compromised? I suspect the flow will be impacted much less that one might intuitively surmise.
Hi Dave, I noticed that most aquarium gravel has a high gloss coating. Does that hinder bacteria growth due to the slippery coating?
In reply to Brad ………..It probably has only a very small effect, based on the fact that lava rock did so poorly in the tests compared to standard aquarium gravel.
Hello Dave,
A quick question on uplift tubes if I may.
I will need to reduce the height of an uplift tube due to some other equipment needing to be installed in the exact position where the tube is located.
Does reducing the height of an uplift tube affect the performance of the UGF? I am using airstones in the tubes & I will be reducing the height from 18 inches to about 9 inches, so roughly half way up the height of the tank instead of at the top.
Many thanks,
John
In reply to John Henry …………. Yes reducing the height of an uplift tube will definitely effect the flow though the undergravel. Have you considered replacing the airstone with a powerhead pump?
I had powerheads on them for a while, but no matter which ones I used I could always hear a slight hum from the motors. For me, the sound of the bubbles was less irritating than the buzz from the powerheads. The air pump that I use is completely silent located inside the enclosed cabinet.
I have a 4ft tank (55 gal) & am running 4 uplift tubes. I’ll leave three of them with the airstones & put one of my small powerheads back on the other tube at the reduced height.
I know that 4 tubes is probably overkill in this situation, but I just want the best efficiency from my system.
I’m about to install a fluidized sump underneath so just want the UGF to perform to the best that it can.
Appreciate your advice….your wealth of knowledge is invaluable & your web pages are a constant source of valuable information. I know everyone appreciates you sharing so much.
Cheers,
John
Dave, I have a 15 gallon tank with a Tidal 35 (replaced media with 30 PPI Poret foam), a sponge filter and a UGF. My problem is that my hard tap water fluctuates around GH 250 (14 drops) but after it’s been in the tank it rises to over 380. The culprit I think was the aquarium gravel. So, I’m slowly removing it and thought I’d replace it with (1st: Caribsea Samurai soil…..but no?) Quartz sand. I’ve removed one lift tube also. My tap water is high GH, lowish KH and 10.0 ppm Phosphate (have crushed coral in Tidal).PH is 7.6. A ton of plants, stem and epiphytes….they seem okay.
Oy vey……..what should I use for a substrate?
Thanks so much. Love the “new” colorful site with your photo!
Eve Taylor
In reply to EBT ……. stop replacing the gravel. It is the crushed coral in the filter that is making your hardness rise
Okay, I’ll take the coral out, that’s no problem. But it’s only been in less than a week and the GH issue has been going on since I started this tank about a year ago. So, I’m confused.But I am not looking forward to stripping the tank down and especially disturbing the crypts. Thanks, Dave.
In reply to EBT You mentioned CO2 injection earlier. CO2 injection tends to screw with all hardness tests. In any case you’re overthinking it. Throw out your hardness test kits and you will probably be just fine.
Dear Dave, I just read my question (below). I will NOT be using quartz sand – or Samurai soil (?). But I could still use a good recommendation for a completely inert gravel. P.S. I am tired of trying to fix one thing and ruining ten. Thanks, as always!
Hi Dave, it’s been a while and I’m amazed by the new revamped website! Thanks to you and your son for preserving this source of truth for freshwater hobbyists.
I have a question about the best media for undergravel filter. I see that you recommended gravels instead of other media including foam. As I understand from your testing, 30ppi foam is way more efficient than gravel in terms of surface area. So is there any shortcomings of using foam for undergravel filter? I’ve been using them in my tank with good results but it’s good to be aware of any potential problems with that.
Also I’ve been planning to have an axolotl tank and in your axolotl page you recommend no fish at all due to potenial gill nipping. Do you think a pleco would do since they may be less likely to nip the axolotl gill?
In reply to longtluu Foam is an excellent material for any undergravel madden type filter. It just takes more imagination for things like plants. And plecos just do their fin nipping at night when you don’t see them. AVOID ALL FISH WITH AXOLOTL, Period.
Hi Dave. I want to share to you two things: i begin a saltwater UGF and a freshwater UGF using 1.3mm sand. Im a brazilian please forgive my bad english. 3 years ago i set up my first UGF, one thing that encourages me is your articles. I have sucess in the first for 2 years, now i had to dismount they because another issues. My favorite aquarium now is a 45 liters set up yl1 year ago with a undergravel filter and a coarse sand, grains about 1mm to 1.5mm 1 and a half inch height above the plates. and it still working very well. I use this tank to show the sistem to my friens, so a i have a good stock about 15 2 inches fish e feed ther closely heavy amounts.
Now, 10 days ago i set an experimental saltwater tank with undergravel filter and 3mm substrate (i already have a saltwater tank set up in the traditional hobby way). I want to share with you the development of this tank in the next months
Hello dave, what ylu think about using a sand (or gravel?) With grain size of 1mm to 1,mm (sieving all grains tjat are less than 1mm size) in a undergravel filter? Another separeted question, can you talh about saltwater undergravel filter?
In reply to Matheus …………Sand that fine will rapidly plug up any undergravel filter. The tanks may a still “work” with a very slow flow but the package won’t be “optimum”. And all that apply to freshwater UGFs should apply to saltwater.
Hi Dave, I have an undergravel filter in one of my tanks that has plants in it.
Am I still able to use root taps in this tank or will all the fertiliser be sucked into the water column?
Thanks, Michael.
In reply to MichaelG ………. Your instinct is correct. All the tab fertilizer will end up in the water column with any UGF.
Dave, thank you for this article on under gravel filters. I have two tanks I will set up with under gravel filters. I plan on using a fired clay aqua soil with particle size ranging from 3 to 5 mm. I know of some aquarium keepers who put the aqua soil into mesh bags with one millimeter openings. They then cap the bags with 1 to 2 inches of sand or gravel. I have fine gravel that is 1 mm in size. Would you mind giving me your thoughts on using only the aqua soil on top of the under gravel plates versus putting the aqua soil in mesh bags and capping the bags with 1 mm gravel?
In reply to aerman six of one, half a dozen of the other. Do not overthink it.
Dave, is there a powerhead you would recommend for use with an under gravel filter? Thanks!
In reply to aerman All powerheads are equally cheap and equally liable to give you problems.
Thank you for your two responses. I laughed when I read that all powerhead are likely to give problems. I have often referenced your article for UGFs. Thank you!