Repair a leaky aquarium but firstly identifying where the leak is. 1. Look around the aquarium for wetness, if the leak is not obvious. 2. Look for metal corners that appear to be serperated from the glass, and for sealant protruding in the corners. 3. Feel around the edges, and if you feel water, move upward from that location, until the surface feels dry. 4. Mark the location of the leak, or where you suspect the leak is, with a felt tip pen.
Scrape the old sealant around the leaking area with a razor scraper. If you are sealing the tank from the inside, be careful not to allow any of the old sealant to drop in the tank.
Apply nontoxic 100% silicone sealant to the leak area. Allow the sealant to dry and cure a minimum of 12 hours, but preferably 24 hours.