I've been on fishlore and a couple of other forums and the question of which silicone to use keeps popping up. Plus people are losing fish so I figured I'd set the record straight. The RIGHT silicone to use is GE Silicone I w/o mold or mildew additives. Those additives will kill the heck out of your fish. I mean absolutely. If you use GE Silicone I Clear it does not have this additive, thus will not ruin your tank/harm your inhabitants. It won't say protects against mold/mildew anywhere like GE Silicone II does. I've used Silicone I Clear on 2 fully un-sealed tanks and after 36 hours of curing then another couple worth of rinsing and dechlorinating they had perfectly healthy fish in them. Just my $0.02, I figured it was time for another post like this. Cheers!