there are many kinds of silicon sealants, for plumbing or metal, and everything under the sun, so there probably is some harmful types that should not be used on aquariums, aswell as some that are just not made strong enough for the task, etc. make sure you buy the correct kind of sealant if you do any work on an aquarium.
we were working with my dads friends shop making tanks we used the tube he had but it had no lable...he died 2 months ago so me and my dad are starting our own little tank biz...In our garage we have all the tools