Silicone II update (bad news)

Seems extremely likely that the mildewcides (FWIW, 'mildewcide' is the only accepted usage, 231 Google hits for 'mildacide' vs. 6,870 for 'mildewcide' speaks for itself) were what killed them, you could test for ammonia and see if it was at astronomical levels...but seems like poisoning to me. Sorry

You should really strip it and start over...clear silicone wouldn't be that visible, would it? I'm sure black would have been more attractive but unless you are willing to pay $10 for 3 oz...I wouldn't be. However, it is on sale, here:
http://www.petco.com/product/104409/All-Glass-Aquarium-Black-Silicone-Aquarium-Sealant.aspx

I would really not feel good about myself if I sacrificed more adult fish to this experiment...but I guess if you have some excess fry you were planning on using as feeders, that might not be such a bad idea. Fry would probably be even more sensitive.

Did you ever fill the tank and empty it before putting in the fish?

I would strip it as well. No sense in wasting money and fish when you know it contains the chemicals.

SILICONE II by GE=wrong one. It'll kill fish especially if you don't let the silicone cure for 24-48 hours DRY after you put it in. You want GE Silicone I Clear because it doesn't have the mold/mildew additive. I've used it on 2 tanks now that had to be completely re-sealed and after 36 hours the tanks were fully established with fish in them.

There is no doubt that GE I Clear is safe to use, that's commonly accepted.

However, the OP wanted black silicone...went on the advice of a fish forum, which said it was ok to use, even though it was not. Even though it said 100% silicone, which as has been explained, simply means that it is undiluted 100% silicone, not acrylic or anything else.

Why GE doesn't label the mildewcides and fungicides in GE II is anyone's guess - I sure would want an explanation, myself. I suppose because they don't realize that people are wanting black silicone for aquarium applications?

Anyway, although I would be mightily ticked off at GE for their improper labeling, and would make sure to let them know how inconvenienced I was because I had to not only reseal, but take apart my aquarium one more unnecessary time, as soon as the OP found out there were mildewcides that should have been the end of the conversation.

I'm sure he realizes that now, and it's a valuable cautionary tale for anyone else who wants cheaper black silicone than what they sell at the LFS (don't we all?)

This reminds me of a question that popped up on another forum...

Someone (a she) paid her brother to fill up her 55 gallon aquarium. No Python, so it was done in bucketfuls. Unfortunately the bucket her brother employed had been used for flea shampoo, and after that, undiluted Lysol.

Can she use activated carbon to remove the toxic chemicals? She asked. Well, to be honest, I didn't really know if activated carbon would work in this case...but even if it did, is it worth the risk? A big fat NO

Sorry to hear that it didn't work.

I tore up the tank yesterday that I had resealed with Silicone II and got some Silicone I to put on. Decided it wasn't worth the risk. While the fish in it are going to be free, the amount of work put into quarantine/acclimation was too much to risk killing them.

I'm actually starting to wonder if my girlfriend's secondhand 75g may have something like this on it. It isn't killing the fish directly, except that the cycle keeps crashing (which is killing fish). The silicone on the sides is black while the bottom is clear so I'm thinking the previous owner may have resealed it. Gonna give it another chance to cycle and then might tear it up for her.

I used DAP brand black silicone window & door for my cork on slate project, haven't ever noticed problems from it. I had to have my True Value hardware order it for me. No mildewcides