That product appears to have a mildewcide, which makes it unsuitable for use in an aquarium. Having 100% silicone on the label doesn't make it safe. You need a product that doesn't contain mildewcide, regard;ess of brand. Usually, anything that says "Kitchen and Bath" or "Tub and Tile" has a mildewcide and shouldn't be used. In the case of GE brand Silicone I, the version that says "Windows and Doors" is safe. As well, there are house brands that will say "safe for aquariums" or even "ideal for aquariums" on the label.
Often times the "not recommended for aquariums" warning is for the benefit of the manufacturer and vendor, which releases them from liability should you use it and have a failure resulting in damage.
I would dismantle that tanks and redo it.
Join a fish club. Don't have one in your area? Start one.