How to Repair an Aquarium Fish Tank

Updated November 21, 2016

Damage to aquariums can occur through routine maintenance. Some damage, such as cracks in the glass walls, can make a mess in your house and threaten the lives of your fish. Fortunately, repairing a cracked aquarium is a simple process with the right equipment, and it is a much cheaper alternative to purchasing a new aquarium.

Remove fish from your damaged aquarium and transfer them to a well-oxygenated temporary tank. Remove all accessories so the aquarium is bare.

Thoroughly dry the aquarium, locate the crack and then carefully align the glass so that both sides of the crack are flush with one another.

Tape one side of the crack with masking tape to hold the glass in place.

Apply a thick bead of aquarium-safe silicone to the un-taped side of the crack. Only use clear silicone sealants and always check to ensure that there are no mildew-inhibiting chemicals in the silicone mix, as they are toxic to fish. Most aquarium-safe sealants will clearly state that they are fish-friendly on the label.

Use the putty knife to help smooth the silicone over the crack to provide a solid seal and help stabilise the glass. Though it may not be aesthetically appealing, it is best to have a solid, thick seal on the tank to ensure that the crack does not reopen in the future.

Allow the silicone sealant to dry according to the recommended time on the instructions and then remove the tape on the opposite side of the crack and repeat the process.

Remove unwanted excess silicone by razor blade once dried.

Fill the repaired aquarium and ensure that the silicone seal is complete and that no further leaks develop before reassembling your fish tank.


Repair aquariums in a well-ventilated room as silicone fumes can be irritating.

Things You'll Need

  • Aquarium-safe silicone
  • Masking tape
  • Putty knife
  • Razor blade
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