I totally understand your situation with that size tank. You're going to stock hundreds if not thousands of dollars worth of livestock into it. Your plan to cover the adhesive with more silicone might work but no one can say for sure. I don't know if silicone will adhere but I guess it will.I have an unpopular opinion, all I did was put construction adhesive ontop of the silicon seal, I really don’t have the funds to have someone reseal my tank or the trust for me to do a 250gal. What if I use aquarium safe black silicone to cover that layer of construction adhesive, I really don’t mind the black outline it’s gonna have. It will keep the original seal, and hopefully cover the construction adhesive completely if not greatly reduce the exposure to the water. I believe it was the fumes of the curing construction adhesive that nuked the nano tank, if it even was that. I still have the adhesive piece I used in there and the goby’s are doing good, all inverts/corals are doing fine. Maybe the introduction of the hippo to the nano caused their death with possibly disease overnight