How to Fix a Crack in a Glass Aquarium

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Whether you have a 55-gallon fish tank or a small fishbowl, a crack in the glass can pose a serious problem. Fortunately, in many cases, fixing a broken fish tank is a fairly easy process that you can complete with just a few basic supplies. Be sure to evaluate the condition of your tank to determine whether it is worth repairing or if you would be better off investing in a new aquarium.

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Repairs might or might not be possible.
Image Credit: Svetlana Gustova / EyeEm/EyeEm/GettyImages

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Reasons a glass aquarium breaks

There are many possible reasons your aquarium may have developed a crack. If the aquarium is on an uneven surface or doesn't have enough cushioning, the heavy weight of the tank and the water can place pressure on the glass, causing it to crack. Heavy or sharp decorations, such as rocks, can also damage the glass, especially if they fall or shift while you are moving the tank. Be sure to take steps to correct these conditions and take care when cleaning to avoid causing a new crack in the glass.

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There are some other reasons a tank can break that may make replacing the tank a safer alternative for your fish. If you have an old tank or one made with cheap materials, the glass may not be thick or strong enough to withstand the water pressure inside the tank. It may also be more prone to breakage when moving and cleaning the tank.

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Empty the tank

Before you can repair a crack in the fish tank, you need to empty the tank. Move the fish to another tank or container. It can take 24 to 48 hours for the sealant to fully dry, so make sure the container is large enough for your fish to live comfortably for this period of time.

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It is a good idea to mark the crack with some masking tape, especially if it is a small crack. This ensures you can easily locate and repair it once the tank is emptied. Drain the water from the tank, taking care to remove the water in a way that doesn't add weight or pressure to the cracked area. Be sure to remove all decorations, plants, and substrate as well. Finally, dry the tank completely with a clean towel.

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Fish tank crack repair

The best fish tank crack paste is an aquarium-safe silicone. Be sure to read the product label and follow the instructions to ensure the crack is sealed properly. If there is sealant from a previous repair, be sure to remove it completely with a razor blade. Then, use a towel and acetone to clean the glass where the crack is located. Applying the silicone to dirty glass may prevent it from fully sealing the crack.

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Apply the aquarium-safe silicone gel to the crack on the inside of the tank. Smooth the sealant with your finger. You can also use a caulking tool if this is easier for you. Allow the sealant to dry completely. This may take up to 48 hours but check the product label to determine the recommended drying time.

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Once the sealant has set, add water back into the tank to make sure the seal holds and the crack no longer leaks. Move the fish back to the tank when you are confident in the repair.

Replace the pane

If the glass has a large crack, you can also consider ordering a new pane rather than replacing the entire tank. Measure the pane precisely to ensure you get the right size. Once the tank is empty and dry, separate the damaged pane and scrape off the old silicone from the exposed edges of the tank and clean them with acetone.

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Apply the silicone gel to the edges of the new pane and position the pane on the tank. Secure it with duct tape to hold it in place. Apply another layer of aquarium-safe silicone gel to the seams on the inside of the tank and allow the sealant to fully dry.

Remove the duct tape and fill the aquarium with water. When you are confident the seal is holding and there are no leaks, you can return the fish to the tank.

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