Ok, this conversation or debate, has been rehashed it seems, almost, since the beginning of time. It is never resolved, and the sound sensible advice, that has been given, is generally ignored, or even further debated.
Is Silicone II toxic? Largely it is an unknown. Most likely, once cured, it is not anymore toxic than any other silicone.
It is however, a neutral cure or solvent based product. It releases an ammonia odor. It is very easy to spot this, with similar products, using a simple sniff test.
Silicone I, on the other hand, is an acetoxy cure product. It releases an acetic acid odor (vinegar.) It is very easy to spot this, with similar products, using a simple sniff test.
Since the beginning of time, the recommendation (regardless of the debates, and the "oh it will be fines",) for silicone in an aquarium application has been:
100% Silicone (most are)
Acetoxy Cure (some are some aren't)
FDA Approved for food contact
Why the FDA approval? Because it eliminates the possibility, (either real or imagined, depending on the particular product,) that the silicone will cause a problem in the tank. It is not that there are no products out there, that are NOT FDA approved, that are safe. It simply takes the guess work out of it. In this manner, the "mass kill-off" will not be related to the silicone, in any way other than insufficient cure time. Because any way you slice it, if it is not FULLY cured, it will kill your tank FDA approved or not. Allowing a week or more cure time eliminates even this variable.
Did the silicone kill off this particular tank? It is an unknown, could it have? Yes, considering the application, it is quite possible that it did not cure--especially in the center of the background. Or it could have been, since the tank should have been taken down, that the shock, when restarted, took out the tank. Or maybe, Silicone II is just toxic from the word go cured or not. But anecdotal information exists supporting BOTH sides of the question, so again it is an unknown.
Also,the labels on both GE I AND II, say not for use in aquariums, however, IIRC, the GE I label (or product information) now shows FDA approval. Be that as it may, the recommendation remains unchanged.
100% Silicone
Acetoxy Cure
FDA Approved ......
This eliminates the questions, and then there is only the question of using the right product for the application. No longer is it needed to ask "is this silicone safe in my tank" and variations thereof. Read the LABEL. Read the product information, you have to look for it sometimes. The MSDS does not tell you what you need to know. The tank builders will not tell you, the tank manufacturers will not tell you. Though, I do have inside information on that, and have posted it many many times. Sometimes the silicone manufacturer will tell you, sometimes they will not. However, if you take the basic advice, there is not going to be any questions, other than is Product A strong enough for the application, or would Product B, considering the application, be a better choice.
