Step-by-Step What to Do if Your Fish Tank Leaks

It’s every aquarium keeper’s worst nightmare—you go to check your tank and find a puddle underneath it. If you’re only slightly unlucky, it’s a small seeping leak that can be repaired. If you’re unlucky, however, you might end up with a miniature waterfall in your bedroom.

So, what can you do if your fish tank is leaking? Depending on the severity of the leak, a fish tank can be either emptied and repaired with silicone sealant or will need to be replaced. It’s also essential to address any water damage that might occur around the aquarium as the result of a leak, such as soaked carpeting or wet electrical outlets.

A leaking fish tank might seem like the biggest catastrophe you can run across when you have an aquarium, but with some preparation and quick thinking, you can save your fish and possibly your tank as well. Keep reading to find out more about aquarium leaks and how to repair them.

What Causes a Fish Tank to Leak?

There are several scenarios (some nightmarish) that can ultimately lead to your fish tank springing a leak. Here are some of the common causes of a leaking fish tank:

Construction defects: While it isn’t a common occurrence, the fact of the matter is that aquariums are made of glass, and glass is fragile. During construction, storage, or transport, fish tanks can develop weak points that become pressurized after being filled with water. These weak points can eventually rupture and lead to a leak or even a tank wall collapse.
Uneven pressure: Uneven pressure can lead to cracks on the bottom of an aquarium, and uneven pressure is caused by a tank’s weight not being evenly distributed across the base of the aquarium, causing part of the aquarium’s base to be weakened. Age can further this weakness to the point that it becomes a stress fracture, and the bottom of the tank eventually leaks.

Damage from décor or hardscape: If hardscape such as boulders or hard driftwood is knocked against the side of the tank’s glass either by a person’s hands or larger fish, this can cause cracks and leaks. Since this kind of damage often occurs in the center of the tank’s glass rather than a seam, it often results in the tank requiring replacement rather than repair.
Damage from a projectile or impact: It happens more often than people usually think—a TV remote or cellphone accidentally goes flying out of someone’s grip, or a child playfully throws a ball across the room and misses their intended target. Suddenly half the tank’s water is on the floor. This is one of the more dire scenarios of a tank leak because it is an immediate danger to the fish.
Weakening sealant from old age: This is one of the most common causes of a tank leak and can often be found in older tanks that are allowed to dry-rot in storage that is not temperature controlled. The shrinking and expanding of sealant in response to temperature fluctuations in a garage or storage unit cause aquarium seals to become weakened, ultimately leading to leaks.

Regardless of whether the leak is the result of natural causes or an accident, aquarium leaks are no joke. Not only do they threaten the well-being of your pets, but they can also result in expensive damage to your floors or electrical outlets.

How to Find a Leak in Your Aquarium

If your tank wall has collapsed or is leaking as the result of a fracture or impact, chances are you know exactly where the leak is coming from, and it isn’t much you can do about it. On the other hand, if you wake up to find a puddle underneath your aquarium and see that the aquarium’s water level has dropped drastically, you’re dealing with a slow leak that is likely originating along with one of the aquarium’s seams.

Evacuating Your Fish in the Event of a Leak

The first order of business when you have a tank leak is to figure out some other place to put your fish while you get the leak situated. A quarantine tank can be a good option for temporarily keeping your fish while you figure out where the tank is leaking from and drain it for repair, but if you don’t have a quarantine tank, a water changing bucket with an air stone can work.

It’s important to remember that, while your fish are out of the main tank, they continue to have oxygen from an air pump. Some live plants from the main tank can also be relocated into the quarantine tank or water change bucket with the fish to help aid with this.

Fish from the main tank should initially be kept in some of the water from the main tank while you establish where the leak is, but you will eventually need to do a water change since the temporary tank does not have an established nitrogen cycle.

How to Tell Where Your Fish Tank is Leaking

Once you’ve removed your fish to safety, the easiest way to tell where the tank leaking is to see how much water is left in the tank.

If the tank has only leaked partially out – then that is an indicator that the leak is likely not in the bottom of the tank or anywhere beneath the current depth of the water.
If the tank is still in the process of leaking – you should be able to see water gathering and dripping down from whichever silicon seal has lost its integrity. Unless you know where the tank is leaking from, it will be difficult to repair it successfully.

After you determine where the leak is, you’ll have to decide whether to empty the tank temporarily and reseal the entire aquarium or attempt to reseal the aquarium from the exterior at the point of the leak. It is generally recommended to drain the tank and reseal it from the inside while it is dry since this leaves you with a much more waterproof and sturdy seal that is less likely to result in another leak.

If you fill the fish tank back up and it continues to lose water, but there is no apparent leak from a seal in the sides of the tank, this means that the defective seal is likely in the tank’s bottom. This is a much more difficult seal to fix without completely draining the tank and resealing the entire thing. In some cases, if the tank is a smaller or cheaper model, it is less of a hassle just to replace the tank and buy a new one.

Step-by-Step Guide to Fixing a Fish Tank Leak

Have a tank leak? Never fear! Read through this step-by-step guide to get a grip on the situation fast to save your fish and your flooring. Navigating a tank leak doesn’t just mean fixing the tank—it also means taking steps to protect your flooring, taking care of your fish, and ensuring electrical safety.

Turn off the power

Make sure that the electrical source to the aquarium’s filter and air pump is unplugged to avoid an electrical shock. Most aquarium equipment is waterproof to a degree, but if you didn’t have a drip loop protecting your outlet, you could have water leaking against the wall. Ensure that the outlet is dry and then unplug everything.

Evacuate the fish.

This is a perfect time to have a quarantine tank ready to go. If you have one, move your fish and main tank water (if you have enough left) over to the temporary tank and set up an air stone to oxygenate that tank. The fish will be fine temporarily without filtration, though they will need it in the form of partial water changes if kept in the temporary tank for any extended length of time. If a quarantine tank isn’t available, a large water change bucket will suffice.

Identify the leak.

This is the point where you determine where the tank is leaking. If it is a large crack or a weakened seal and the tank is still in the process of leaking, the source of the water leak should be reasonably obvious. If the majority of the water has leaked onto the floor, you will need to inspect the entire tank to find where the leak is.

Take care of the floor.

As you can imagine, gallons of aquarium water in a carpet and the padding beneath a carpet is a recipe for mold and other structural problems. Ideally, the carpet would be able to be pulled up, and the subfloor padding allowed to air dry with the help of fans and dehumidifiers. If this is not possible, as much of the aquarium water should be soaked up with towels as possible, and large fans should be run on the area for at least a week.

Drain the tank.

The best way to reseal an aquarium is from the interior, and to reseal the inside of the tank, it has to be emptied, cleaned out, and dried. If you’re going to this extent, it can be a good idea to go ahead and reseal the entire aquarium at once. If one seal is weak and leaking, the others are likely the same age and close to being structurally weak as well.

Apply silicone sealant.

This sealant must cure for several hours before the tank can be refilled with water again. Not only does this allow it to harden and prevent new leaks, but it also prevents chemical residue from the sealant leeching into the water and poisoning the fish when they’re returned to the aquarium.

Return fish to the aquarium.

Once the fish tank’s new seals have completely cured, the tank’s substrate, décor, plants, and fish can be returned to the tank. It should only take a few hours for any debris to settle and the tank to regain its former clarity.

Monitor the water parameters.

Since you likely had to do substantial water changes in the course of draining your tank and refilling it for your fish, chances are your water parameters have shifted. Following the repair of a leak, you should observe your fish note any changes in behavior and make sure that ammonia levels remain low. Make sure to test the water with a water testing kit.

As long as it is a slow leak and not a major collapse, a leaking fish tank can usually be repaired with only some inconvenience to the fish keeper and some minor discomfort to the fish. But if you have a blow out in your tank, you might find yourself scrambling to keep your tank’s stock swimming while you rig up a tank repair (or go out shopping for a new one).

The Kind of Fish Tank Leaks That Can’t Be Fixed

A leaking seal on an aquarium can usually be repaired even if the process is messy, time-consuming, and inconvenient. But occasionally, a flaw in the glass of an aquarium (either a natural defect caused by construction or a small stress fracture caused by impact damage) can be enough for a tank’s wall to collapse under the weight of the water within it.

This can lead to a waterfall effect that aquarium owners can only hope happens when they’re at home and ready to have all hands on deck to save their fish and their flooring. An aquarium that cracks to this extent can’t be saved without replacing an entire plane of glass. Most people in this situation end up having to buy a new aquarium altogether.

A crack that occurs anywhere across the plane of the aquarium’s glass usually can’t be resealed because the weak point will always cause uneven pressure in the aquarium that will threaten to break the glass again.

The only aquarium leaks that can be repaired with any kind of success are weakened seams on the aquarium, and even this can be an iffy operation if the seam is on an aquarium’s bottom.

Best Silicone Sealant for Aquarium Leaks

There are many different kinds of silicone sealants available to repair aquarium leaks. The best ones will typically be clear, non-toxic, and fast-drying (some black varieties are available). Once a silicone sealant has been allowed to cure completely and has been applied evenly along with all weak seals on the aquarium’s interior, it should prevent any new leaks from forming for years to come.

Here are some of the best silicone sealants you can use to fix a leak in your aquarium:

ASI Clear Aquarium Silicone Sealant

Sil Bond Food Grade Silicone Sealant

All silicone sealants are applied with basically the same procedure:

Clean and dry the surface as much as you can.

Wait for it to dry completely.
Apply the silicone sealant in a smooth, even line along with the interior of the aquarium seam. To provide a waterproofing effect, this seal must be applied in an unbroken line.
After the silicone sealant is applied, allow it to cure completely.

If an older aquarium is being acquired on the used market, it’s a good idea to clean and reseal the aquarium before adding water to it to help ensure that it is watertight.

How to Care for Fish During a Fish Tank Leak

A tank leak can be traumatic for fish depending on how much water leaks out of the tank at once, and several issues can occur simultaneously:

The amount of relative ammonia in the water spikes because of more fish in a much smaller amount of water. This is especially true if water leaked out overnight, and you weren’t aware of the leak for hours.
The fish are under stress—they understand the water levels are dropping, and this stimulates them to try and migrate to deeper waters, but in a glass aquarium, there is nowhere to go.
Oxygen levels are dropping rapidly. Less water means less dissolved oxygen available for the fish in the tank, and once the water drops below a certain point, they often use circulation via the filtration system and air pump as well.

If you discover a leaking tank after several hours and the water level is very low, your priority should be to lessen the stress on your fish by following these steps:

Quickly fill up a backup container such as a water change bucket or quarantine tank with water.
Dechlorinate the water.

Bring it up to ambient temperature with an aquatic heater as quickly as possible, adding an air stone to increase the levels of dissolved oxygen. A water conditioner can also be used to reduce stress.
Using a net, catch the fish from the main tank and move them into the temporary tank. Some more shy species may be in hiding if the leak has been going on for several hours, so be sure to go through the substrate carefully and check all plants and décor for fish that are hiding out.
This is also an excellent time to do a headcount and make sure that no fish has jumped out of the tank.

Since, in many cases, you’ll be draining the tank completely to reseal it if you’re repairing a leaking seam, you’ll need to make sure all of the fish are safely evacuated before you remove the remainder of the water.

This can be a very traumatic event for fish, and more fragile fish may not be able to survive the transition from the main tank to a temporary tank if the water parameters in the new tank are too dramatically different than the main tank. To prevent shock from occurring in the fish as a result of this, add as much of the original tank water to the temporary tank as possible and regulate the water temperature.

How to Care for Fish After a Fish Tank Leak

After you are forced to replace the majority of the water in a tank (either by re-sealing the tank and then setting it back up or replacing the tank and setting it back up) there is a high chance that you’ll have to deal with some water chemistry fluctuations as your beneficial bacteria rebounds from the loss of the original tank water.

If you made sure to keep your filter media wet during the process of replacing or repairing the tank, you should have retained the majority of your beneficial bacteria colony, and you should be able to jump-start the nitrogen cycle in your tank quickly. However, water chemistry should be monitored carefully for a few days after the tank is refilled to ensure that there are no spikes in ammonia or nitrites.

The process of a tank leak can scare fish, and this, in turn, can lower their immune systems and make them more susceptible to illness. To avoid this, it’s a good idea to keep the lights in the tank dimmed for a day or two following restoration and keeping the environment around the tank calm and quiet. This can help fish relax after their ordeal and restore order to the tank.

How to Care for Your Floor After a Fish Tank Leak

Almost as important as what you’re going to do with your leaking tank when you develop a tank leak is what you’re going to do with your floor. Only the luckiest of aquarium owners end up with a leak on tile flooring—the majority end up soaking a carpet or hardwood floor.

In either case, the news isn’t great—aquarium water can cause severe damage to either carpeting or wood flooring. After ensuring the safety of your fish, the biggest challenge you face when trying to fix a fish tank leak is mitigating the damage of anywhere from a few to fifty gallons of water soaking into your floor.

If you soak your carpeting with a fish tank leak, here’s what you need to do:

Get a wet vac to suck up as much water out of the carpet as possible. It also helps to take tons of towels and walk across them to try and get up as much of the moisture out of the carpet as you can.
Pull up the carpet if possible and get some kind airflow between the carpet and the padding beneath it. This is an essential aspect of trying to manage water damage from a leaking aquarium since ventilation is crucial for preventing the growth of mold. If too much water has soaked into the padding beneath the carpet, it may be best to replace it entirely.
Use dehumidifiers and box fans to create circulation. This will help remove moisture through evaporation and also help prevent mold from forming. Do not use space heaters or any form of heat, as this can make water damage worse in some cases.

Steam clean the carpet thoroughly after drying to prevent any mildew smells. This should be done repeatedly to prevent the formation of mold or bacteria caused by stagnant moisture underneath the carpet.

If you have hardwood flooring rather than carpeting that has been soaked by a fish tank leak, here’s what you need to do:

Remove any waterlogged objects from the floor. These can cause water to gather on the surface of the wood underneath them and penetrate the varnish, causing rings and other disfiguring marks to the hardwood.
Repeatedly use a wet vac over the floor even after it appears dry, being sure to go over seams between wood planks carefully. Keep going over the floor with the wet vac until it appears that no new moisture is collecting in the vacuum’s canister. well explained in this video.
Disinfect the floors with a floor cleaner. The addition of water to latent debris and bacteria on the floor can make any water-based damage worse.

Leave fans and dehumidifiers running for at least a week or until a moisture meter shows that there is no residual moisture left in the hardwood where the tank leak occurred.

Depending on how much water ended up on the floor, making sure that it all gets cleaned up can be the difference between a temporary inconvenience and lasting damage to your home. Fish tanks can be easily replaced—hardwood flooring and carpeting less so.

If you have a fish tank, it can be a good idea to keep dehumidifiers (see price range on Amazon, isn’t so expensive) and fans on hand in case of a leak. While they only happen rarely, being able to react to them efficiently can be the difference between being able to clean them up effectively or not.

Fixing a Fish Tank Leak is About Damage Control

Once your fish tank has sprung a leak, trying to determine the cause of the leak is secondary to keeping the fish alive and making sure that you don’t end up with permanent damage to the interior of your home. If you have the equipment on hand to move quickly to remove the water and re-seal the glass, you can address a fish tank leak with minimal damage to both your fish and your floor.