Would using silicone to seal a pond be toxic to goldfish or plants?
Silicone with mildewcides for bathroom use would NOT be safe in the pond, or aquarium either. Mixed silicone caulks, anything less than 100% would not be safe. Only the pure silicone sealants that say they are suitable for aquarium use are sure to be safe. Sone, like GE Silicone I, has some distilates and other ingredients that could pose a problem, but many aquarists have built or repaired tanks with Silicone I and had no problems they noticed. If they had built a large tank things might have been different since GE Silicone I is not as strong as the aquarium silicones I’ve seen. People have even used Silicone II which emits ammonia, very toxic to fish, while curing. It has less holding strength than Silicone I and some aquarists have not noticed problems with it. But using an unsuitable product hoping to be lucky is like crossing the road blindfolded. Just because you made it across does not make it safe. Even the right silicone is a dubious pond sealant. Silicone does not stick well
