i have a thirty gallon tank and i have it set up, and cycled but yesterday i noticed a crack in the corner of my tank. id rather not take the water out is there a silicone i could use for underwater?
If the crack is in the seam itself, it can re repaired..if it's in the glass, then don't use the tank as an aquarium..buy a new one. Better safe than sorry. If that crack is in the glass pane, believe me, you'll be worried about it constantly, do yourself a favor and ditch the tank.