Ways to Fix a Crack in a Fish Tank

Cracked fish tanks can create a disaster, particularly if they contain a great deal of water. The vast majority of modern aquariums are made of glass panes and silicone sealer and cracks can develop either in the silicone or in the glass pane. Water pressure increases with height and cracked glass panes in tall tanks are best removed and replaced. Cracks in shallow and small aquariums are typically repaired by simply draining part of the water and using fresh silicone to carry out the repair.

  1. Cracks In the Silicone

    • Old silicone, or incorrectly applied silicone, sometimes develops cracks. Select fish, such as triggerfish and puffers, bite at and weaken silicone seals as well. Cracks in the silicone, which appear near the top of the aquarium, can be repaired while the tank is still half full of water. These aquariums can be drained to a few inches below the cracked silicone, which must subsequently be removed with a sharp blade. The glass is best cleaned with a cloth containing acetone and thoroughly dried. Aquarists need to wait 24 hours after applying the new silicone, before they can fill the aquarium again.

    Tiny Cracks in Small Aquariums

    • Small cracks in aquariums of 10 gallons and smaller can be repaired by simply smearing a bead of silicone sealer over the crack, on the inside of the aquarium. The aquarium should first be drained and dried. Use acetone or white vinegar to clean the area, which must be dried prior to the application of the sealer. The thin bead of silicone sealer must be carefully smoothed over the crack and allowed to cure for at least 24 hours. This type of repair is only suitable for very tiny cracks in small aquariums.

    Larger Cracks in Small Aquariums

    • There is far less pressure on the glass panes of small and shallow aquariums, than on the glass of much larger tanks. A cracked pane in aquariums of 25 gallons or less can be repaired by placing another piece of glass, similar in size, over the original, cracked piece. This approach saves the aquarist having to remove the silicone sealer in order to completely replace the cracked pane. The aquarium must be drained for this repair and the cracked pane must be thoroughly cleaned with acetone. The new glass pane, which must be thoroughly smeared with silicone on the contact side, is then sealed to the original, cracked pane.

    Long Cracks in Large Aquariums

    • Long cracks in the glass of large and tall aquariums can normally not be fixed. In these cases, the glass pane must be removed completely and replaced with a new pane. The aquarium will need to be drained completely and the substrate must be removed. The original silicone sealer must be stripped away and all the glass surfaces that require bonding with new silicone must be wiped down with acetone or vinegar. The new pane of glass can be held in place with masking tape after the silicone has been applied and the pane is in position. The hobbyist will need to wait for at least 24 hours before filling the aquarium.