Adding liquid rubber or pond coat to the tank at this point in the build will only complicate the problem. As other have already stated, the old silicone need to be removed, check the build to be sure there are no structual issues, and reseal the glass. Make sure you have sanded the resin to give the silicone something to bite to. When putting down the silicone, you want to come as close as you can to getting a continuous bead of silicone. The fewer times you lift up the caulking gun the better! Good Luck!
