A lot of people have been asking about silicone for the aquariums. Going by the many recommendations across the internet I used GE 100% Silicone 1. After someone pointed out to me the under the instructions it says "Not for underwater/aquarium use", for my own peace of mind, I contacted Momentive (manufacturer who makes it for GE). Their response was: "We would recommend removing the silicone. It is not designed for aquarium/below water line use because it may fail when submerged for continual use and harm your fish". What they mean by fail, I don't know, breakdown, crumble, lose adhesion? Since it's not in a critical area (used to glue a divider in a tank), I'm going to just keep an eye on it, but I will not be using it again in any of my aquariums. Take it or leave it, this is my opinion.