Comments on: 14.12. Silicone

By: David Bogert

David Bogert — Tue, 10 Feb 2026 23:21:57 +0000

In reply to William King ………. Many thanks for the heads up. I have incorporated your comment wholesale into the body of this article.

By: William King

William King — Tue, 10 Feb 2026 03:25:52 +0000

GE SCS1200 Silicone Construction Sealant might be great for between glass plates but only aquarium-approved silicone should be used on tank interiors.
Aquarium-safe-branded silicones have 0.2% or less D4 (octamethylcyclotetrasiloxane) by weight. Regular silicones such as GE Silicone I contain 1-5% D4, up to 25 times more D4. (I believe that D4 is an impurity of the silicone-manufacturing process).
Studies on D4 have shown extremely low quantities limit fish growth, reproduction, and decreases health and it isn’t good for humans either. D4 also bioaccumulates so it’s like lead or arsenic in drinking water, you don’t notice the effect immediately but eventually…. For ≤1g rainbow trout, the lowest concentration of D4 that causes 50% mortality, called LD/LC50, in an acute test is only 0.01 mg/L, which is 1 part out of 100 million. Acute tests only last 24, 48, or 96 hours.
A 10.2 oz cartridge of ASI Aquarium Silicone is currently ~$12 on Amazon with the potential of free shipping so the cost difference between aquarium-branded silicone and construction-grade silicones like GE Silicone I is negligible.

By: Dave

Dave — Sun, 07 Jul 2024 18:57:58 +0000

In reply to Ben z.

In reply to Ben z …. personally I’ve never had a tank fail catastrophically. I’ve only had “drip” leaks. And I’ve never run across any data on the topic. So I don’t have any answers to your questions.

By: Ben z

Ben z — Sat, 06 Jul 2024 13:29:52 +0000

A quick question about aquarium joint failures. Which is more common, is it the glass/silicone bond that breaks, or is it the silicone itself that fails from strain? What about the propagation of microscopic or even (tiny) visible cracks in the glass over time, how would that affect the structural integrity of the joint?

Ive been wondering if it’s wise to have something like a granite plate that’s been properly lapped flat to support truly large aquariums. I recall you told me last year about testing for gaps between the base and the stand with a one-thou shim without water in the tank. But I’m not sure that’s enough peace of mind if the aquarium in question weighs something like 5000 kg.

By: Dave

Dave — Sat, 23 Sep 2023 00:58:42 +0000

In reply to steven han. In reply to steven .... Gaps looking down from the top shouldn't be much of a concern. I would go ahead and leak test it.

By: steven han

steven han — Fri, 22 Sep 2023 19:52:46 +0000

Recently purchased a seapora branded 120 gallon tank (48x24x24).

Upon setting up, I noticed that in the back left corner, where the bottom exterior trim (what the tank sits on) meets at a 90 degree angle , there is a small gap when looking down from the top, but noticeable. I believe silicone is what covers this on all 4 external bottom corners normally and so not sure if this is merely a visual issue, or something to be concerned with structurally?

Again, brand new tank, and not sure if to bring back and exchange or if something not to be concerned with

By: Dave

Dave — Sat, 27 May 2023 02:02:38 +0000

In reply to Kristi Curry. In reply to Kristy ..... There is no good way to seal a galvanized tank. I'd simply buy a plastic stock tank.

By: Kristi Curry

Kristi Curry — Sat, 27 May 2023 01:11:36 +0000

Not sure I’m putting this question in the right place. Recently bought a 100 gallon stock tank (galvanized) for use as a water feature on my deck. I plan to put fish in there. Did some reading about how to prepare it and learned that they often leak, so decided the best approach would be to spray the inside with flexseal.
I thought I built up a good coating around the bottom seam, but when I filled it, found it has a slow leak there. Not sure how to fix this, or if I should even try. A few more coats of flexseal? Or would a silicone bead around the bottom seam work? Would it adhere to the flex seal? What about flex tape? I’d be happy if it got me through the summer. When I take it down this fall, I could do a more thorough repair.
Or should I ask for a replacement? If I got a new tank, should I silicone the bottom seam first and then apply flexseal? Also what exact brand/s of product would I need? Thanks Dave!