How to Repair  a Leaking Glass Aquarium?

Glass aquariums brighten up any room, especially if they contain colorful fish and other lovely aquatic residents. Leaks are, however, quite common with these tanks, where they are majorly caused by flaws in the sealant.

This failure can occur either during the construction of the tank or where it gets weak over time. Leaks of a pin-hole size result in an empty aquarium or a soaked carpet or wet floor.

Such leaks can be fixed externally without needing to tear the entire tank apart.

How to Repair  a Leaking Glass Aquarium?

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How to Repair  a Leaking Glass Aquarium?

Things You Will Need to Repair Aquarium

  • Aquarium-safe sealant. The clear silicone is best suited for repairs. Some silicone brands will have chemicals that discourage the development of mildew, and they are harmful to fish species.
  • Single-edged razor blades. You can easily get these at hardware shops and a paint supply. A blade holder is also functional to buy, although it will be better to use the blades alone at corners.
  • A supply of paper towels
  • Small flat-head screwdriver
  • Needlenose pliers
  • A washable felt-tip marker
  • Acetone

Finding the Leak

The first step is spotting the actual leak. The water level will mostly reduce down to the leak, and not any further. Another method involves wrapping some paper towel or newspaper around the aquarium and checking it for any wet areas. Mark the spot on the tank to narrow down the exact source of the leak.

This process will also be easier if you already understand how glass aquariums are built. Typically, the watertight integrity and the structural integrity of the tank is reinforced where the glass interacts with the glass.

The silicone is spread out where the glass panels meet. A well-built tank will have no flaws or bubbles in the silicone.

Most people will assume the leak is where you can see water on the outside of the aquarium, but they soon find out it is not as easy as that.

For poorly-constructed or old aquariums, the silicone can be observed curling up or separating from the glass in the tank. Start with the sealant if you detect some silicone damage.

Glass aquarium leaks sometimes manifest as a tiny jet of water shooting from a silicone seam. You can use colored water to find the leak if you can not see any damage to the tank’s silicone behind the stream.

Use a syringe to plunge the colored water into the silicone where water is streaming out. The water will follow a tunnel back to the origin of the leak.

In case you have a fast leak, you need to relocate your fish and plants quickly. Look for a container that is free from soap and other residues and drain the tank water.

Keep in mind that aquatic pets get stressed out when water parameters are changed quickly. A slow leak will give you time to look for it and move the aquatic residents more carefully.

Prepare the Aquarium

Once you are aware of the location of the leak, you can then know how to deal with it. Drain the water so that the leaky area is no longer submerged and dry it.

A leak at the bottom of the tank will require you to drain all water as well as aquarium rocks. The fish and plants will need a temporary tank if you remove all the water.

The tank should be thoroughly dried before attempting any repairs. Depending on the severity of your aquarium’s leak, your aquatic plants and fish may have to stay in the holding tank for several days, and you need to plan for such an occurrence.

Remove the Old Sealant

If the leak is larger than a pinhole, you can progress to removing the old sealant. A razor blade scraper is often recommended to do the job since it is easy to use and will not damage the tank.

Remove the sealant a few inches on either side of the leak.

Run the scraper between the two pieces of glass, and press out on the vertical blade with firm pressure at the bottom. You can also use other equipment like small screwdrivers to get as much silicone as you can.

Removing the sealant on corners can be a bit challenging. You may need needlenose pliers to grab a piece of the sealant and pull it away.

Some aquarists prefer to remove just the silicone around the leaking area and leave out the one between the glass panes. Silicone sometimes does not blend well with old silicone, which is why it is sometimes better to do the whole thing.

Clean the Area

New silicone is not effective in dirty areas, and you need to clean the region around the leak.

Use a cloth soaked in some acetone to wipe the remnants of the old silicone and any dirt. Refrain from using Varsol and other solvents that leave a residue.

It is recommended to progress outside and up-wind to avoid inhaling the volatile acetone.

Seal the Leak

You should use a nontoxic 100% silicone sealant on the leak. It is best to consult a professional aquarist to get the most suitable repair items. The silicone should be labeled “100%” silicone” and “non-toxic.” It should also be a High Modulus Product and have no fungicide in it.

Run a bead of the sealant along the leak region using a caulking gun. You can use the gun or your finger to smooth the bead out so that completely covers the leaking seam.

Repairs made on the inside are more effective than those made on the outside. An internal repair will last for longer because water pressure will “tighten” the resulting seal pressing the silicone against the tank’s glass. In the case of repairs made on the outside, the water forces the silicone away from the glass.

The applied silicone should dry and cure for at least 24 hours. The period is longer in a cool and dry area. The silicone will attach securely to the glass to ensure it does not leak. the silicone that has not completely dried will subsequently peel and leak after water is added.

If you desire to expedite the drying process, use a portable heat source like a heat lamp but do not apply temperatures over 110 °F.

Re-check the Tank for Leaks

When refilling the tank, fill it past the area where the leak was. The water’s weight and pressure are other factors to be considered, so wait an hour before adding more water.

If you cannot spot any leaks, fill the tank to the average amount and give it more time.

You can also wrap some paper towel along the area where the leak was and check for wet spots. Keep a bucket close to the aquarium in case of continued leakage.

If you detect a leak, however, you will have to restart the entire process or buy another aquarium altogether.

Only place back the contents of the tank if you are 100% certain the leak has been fixed. Start with gravel and other contents of the bottom area and any chemicals necessary. You can choose to clean the tank’s contents to start with a healthy aquarium.

Locating Hard-to-Find Leaks

Most aquarists suspect a leak when the water level in their tanks begins to drop. Evaporation is not noticeable in aquariums, which is why you should start looking for leaks when you notice a level drop.

A severe leak is easier to locate by glancing around the setup. Another indication is unexplained water around your tank.

Sometimes the leak is not very obvious, and it is bound to frustrate any fish-keeper. Check for sealant protruding in the corners or metal corners that look separated from the glass.

Feel around the tank’s edges for water and then move upward from that area until it feels dry. The furthest location towards the top of the aquarium that is wet is probably the leaking area.

It is important to mark the leaking area with a felt tip pen. You will be able to spot it easier as you progress with repairs. A glass cleaner will easily remove such marks on the glass.

Know the Types of Leaks

Leaks that occur along the seams of your tank are fairly easy to repair because they result from failure in silicone, which is easily replaced.

Other leaks are caused by a cracked bottom or side of the aquarium, and they need more expertise. Replacing a tank’s glass panel will be best done by an aquarium professional.

A pinhole leak can sometimes be fixed with a dab of silicone. Smooth out the dab with a wet finger. Silicone, however, does not mix well with old silicone, and this kind of repair will likely not hold for long.

Common Mistakes when Repairing Leaks

  • Ensure you use a suitable silicone sealant. Look out for a nontoxic and 100% silicone sealant recommended for aquarium use.
  • Not narrowing down on the exact leaking spot. There will always be water at the bottom of the tank, and the leak may be higher or on the sides along the seam or joint.
  • Not cleaning and prepping the glass area well enough before doing repairs.
  • Other aquarists will not repair the entire area of the leak by missing some spots up, down, or around.
  • Not using adequate silicone sealant or allowing it to dry completely.
  • Making repairs in a humid environment is not advised. Duct tape will typically not stick to glass under humid conditions. The glass can thus move before the silicone can settle. The silicone curing process is also slow in humid conditions.
  • Not aligning the glass pane edges evenly together.
  • The tank should sit on a flat repairing surface to avoid cracks and breakages.

How to Prevent Aquarium Leaks?

An aquarium is a substantial investment, which is why you need to safeguard its integrity. You can avoid leaks by:

– Handle with Care

A glass tank is quite fragile, and it needs to be protected after purchase and during installation.

Get someone to assist you in getting the aquarium from the pet store, as more than two hands are always better. The person can open and close doors and clear other hurdles.

Do not squeeze the tank in your car, and ensure there is plenty of space to transport it. Bring cushioning materials like blankets and foam sheets when buying the tank.

These materials will protect the aquarium if it shifts or comes into contact with anything else in your car as you are driving.

– Do a test fill-up

Place the new tank where leaking water poses no harm like the garage. Fill the tank and leave it for 24 hours, after which you should check for any indication of leaks. Only start using the tank if you are confident it is leak-free.

– Secure the Rocks

Any rocks you add to the aquarium have the potential of damaging the bottom pane. To prevent this, add a thin substrate layer to cushion the glass from the pane. Add more substrate round the foundational layer to achieve the ideal depth. This stable rockwork base will be secure from burrowing aquatic species.

– Accommodate a Sump Overflow

In the case of an aquatic system with a sump, ensure it is large enough to accommodate any backflow of water. Such events are common when there is pump failure or power outages.

You can also drill a small hole in the system’s return nozzle just above the water surface.  This action will break the siphon as soon as pumping power is lost such that the pump will only work with the water that remains in the pipe or return hose.

– Schedule Routine Leak Inspections

Leak inspections can be done once a week to ensure your aquarium is working efficiently. Run your fingers along all clamps, hoses, connections, seams, and pipes in your system to feel if any of them is wet.


Glass aquariums are prone to leaks, some of which you can easily repair yourself. Locating the source of the leak is the first step before you attempt any repairs.

The weakening of the silicone sealant will cause most small leaks, and the next step is to remove the old silicone. Silicone does not blend well with old silicone.

Let the silicone you apply dry completely and do a test fill-up to ensure the leak has been effectively sealed.

Inspect your system for leaks regularly as small leaks will eventually result in substantial damage.

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