5 Ways To Fix A Fish Tank Leaking From The Bottom

As you pass by your home aquarium, you notice that the water level seems unusually low. After quickly inspecting it, you discover a small leak at the bottom. So, in a panic, you run to add more water, but before you add fuel to the fire, take a moment to stop, assess the situation, and figure out how to fix a fish tank leaking from the bottom.

Although it’s not uncommon for fish tanks to leak, it does indicate that your tank is either damaged or flawed in design. In this article, we’ll explain why your fish tank could be leaking and then guide you through the process of diagnosing and fixing the problem. So, before you go out and buy a new fish tank, keep reading to learn how to handle the situation.

Are Fish Tank Leaks Common?

Although not exactly “common,” fish tank leaks are not unheard of. In fact, it’s estimated that 1 in 4 fish tanks will develop a leak at some point, and even institutional aquariums, such as the Exeter Aquatic Center deal with leaky tanks. So, if your tank is leaking, don’t feel too bad about the situation—it’s pretty normal, especially with older tanks.

Generally speaking, tanks start to leak as their seals deteriorate. Over time, fluctuations in water pH can eat away at the seals, or they may just dry out in certain environmental conditions. Regardless of why it happens, though, expect your tank to leak at some point as it ages.

How Do You Spot a Leak in a Fish Tank?

The most obvious sign that your fish tank has sprung a leak is if the water level suddenly drops below where it should be. If you ever notice that the water level is lower than normal, inspect the tank for any cracks, holes, or gaps along the edges or around the base of the tank. These are the most likely places for a fish tank to leak.

Another sign of a leaky aquarium is if you find water pooling around the base. Even if the crack, gap, or hole is relatively small, water will find a way to seep through and flood the area around it. In this case, you may have to remove the fish, drain the tank, and then slowly add a small amount of water to locate where the water is draining.

Finally, if you notice your fish acting strangely, it could indicate a small leak in their tank. As fish tanks start to lose water, the quality of the aquatic environment declines, putting stress on your fish, and leading to health problems. So, if they become sluggish or seem to struggle in their environment, a small leak could be affecting the pH balance in your tank.

Cremecicle Lyretail Molly (Poecilia latipinna) swimming in planted tropical fish tank

Why is My Fish Tank Leaking from the Bottom?

There are many reasons why your fish tank could be leaking from the bottom. The exact cause will depend on your specific tank, but some of the most common reasons include:

Cracks or Holes in the Glass or Acrylic

Aquarium leaks are sometimes caused by small cracks or holes in the glass or acrylic. Over time, the constant exposure to water can weaken or wear away the material, leading to deterioration. In some cases, you may be able to see the cracks with the naked eye, but in other cases, you may need a flashlight to spot them.

A Faulty Sealant

When manufacturers build fish tanks, they use an industrial sealant to help create a watertight connection and prevent leaks. However, over time, the sealant can erode, allowing water to seep through. In some cases, you may be able to see if the sealant is no longer effective, but in other cases, you may have to drain the tank and slowly add water to find the leak.

A Broken or Cracked Aquarium Stand

If the stand is not properly supporting the weight of the fish tank, it can crack or break, causing your aquarium to sit off-kilter and leak water. If this is the case, you can simply replace the stand and it should fix the problem. We recommend using a level to test the stand if you cannot find obvious signs of damage.

A Problem with the Aquarium Filter

If your aquarium’s filter is not properly sealed, it can allow water to seep through and leak from the tank. In some cases, you may be able to see or hear the filter spewing water from the tank, but if it’s only just starting to break down, you may have to experiment by removing or replacing the filter.

Faulty Hose Connections Create Stress Points

If any of the hoses or tubing that connect to your aquarium are not properly sealed, they can create high-pressure points, crack the surrounding glass, and allow water to escape the tank. In most cases, you should be able to see if the tubing is not properly sealed, but if not, try disconnecting and then reconnecting each piece to locate cracks and see if that solves the problem.

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How Do I Fix a Leaking Fish Tank?

Depending on the cause of the leak, you can use the following tips to repair and restore your tank to proper working condition. However, if your tank is severely damaged or quite old, it may be easier to replace it rather than risk further damage down the line.

Clean and Inspect the Tank

The first step is to clean and inspect the tank for any damage or cracks in the sealant. Safely remove your fish, place them in bags of water, and then inspect the sealant and glass around the base of the tank for any signs of deterioration. If you still cannot find the leak, slowly add water to the tank and look for any drips or leaks.

Replace the Sealant

If the sealant around the base of your tank is no longer effective, you can try to replace it. Begin by draining the tank and then removing any old sealant with a putty knife. Once the area is clean, apply a new layer of sealant and allow it to dry for 24 hours.

After refilling the tank, mark the waterline and wait a couple of hours to see if any water leaks from the tank. If it does, add more sealant and check the glass for signs of physical damage.

Replace the Aquarium Stand

If the stand is cracked or broken, you can try to replace it. Begin by draining the tank and then carefully removing the fish. Next, remove the old stand and then add the new one. As you’re installing the new stand, use a level to guarantee that it’s sitting flush against the table or floor. This will help to prevent spills and new leaks.  

Replace the Filter

If the filter was improperly sealed, you could try replacing it. Begin by disconnecting the old filter and removing it from the tank. Next, add a new filter and make sure that it’s properly installed before adding water back into the tank. The seal ring should be placed so that it stays moist, or it will dry up and crack, leading to new leaks later on.

Reseal the Hose Connections

If any of the hose connections were not properly sealed, you could try to reseal them with aquarium-safe silicone. Begin by disconnecting the hoses and then removing them from the tank. Next, apply a small amount of silicone to the connections and then reattach the hoses. Wait for the sealant to dry before adding water, and then test the seal.

If any water leaks from the tank, immediately drain it and apply more sealant to avoid creating new stress points. If you find that the glass has already cracked after disconnecting the old hoses, you may have to replace the tank entirely.

How to Care for Fish During a Fish Tank Leak

If your fish tank has been leaking for some time, your fish may need some special care to help them adjust during and after the tank repair. Using these tips, you can guarantee that your fish stay healthy and survive the transition.

Move the Fish to a Safe Environment

As soon as you notice that your fish tank is leaking, remove your fish and place them in a safe environment, such as a large bucket or another fish tank. As you are removing your fish, use a net to avoid stressing them out, and be sure to add an air stone to their new temporary home to help keep the water oxygenated.

Match the Water Conditions

Ideally, you should try to match the water conditions in their temporary home to that of a healthy aquarium environment. This includes water temperature, pH, and hardness. To do this, you can use a water testing kit and then add the appropriate chemicals to the new tank. You’ll likely have everything you need to do this but if not, speak with your local pet or aquarium supply store.

Monitor Your Fish

Once your fish are in the new tank, monitor them closely for any signs of stress or illness. If they seem to be struggling, you may need to increase the aeration or change the water more frequently. In some cases, you may need to consult a vet to ensure that your fish are healthy and to rule out any underlying health problems.

Control the Amount of Light Around Your Fish

Too much light can stress your fish so if possible, try to maintain the amount of light in their environment. This may mean setting up their tank in a dark room or using a light timer to regulate the amount of time they’re exposed to light each day.

Avoid Overfeeding Your Fish

Although you may be tempted to feed them more during this stressful time, resist the urge to overfeed your fish. When fish are stressed, they tend to lose their appetite, so if you overfeed them, the uneaten food will decompose and pollute the water. Instead, feed them small amounts several times a day to help them adjust.

Frequently Asked Questions

Can You Fix a Fish Tank Without Draining It?

If the leak is close to the top of your fish tank, you may be able to fix it without draining the entire tank. However, if your tank is leaking from the bottom, it’s best to completely drain the tank and then fix the problem from the inside of the tank.

Should I Apply Sealant to the Inside or Outside of the Tank?

It’s best to fix cracks or leaks from the inside of the fish tank. This will help to create a seal that’s level with the inner surface, preventing points of variable pressure from creating stress on the glass.

Can I Use Flex Seal to Fix a Leaking Fish Tank?

Flex Seal is safe to use in aquariums but always make sure it has dried before refilling your aquarium. Additionally, it may be toxic to your fish if they start to eat the seal and your tank.

What is the Best Way to Prevent Fish Tank Leaks?

The best way to prevent fish tank leaks is to regularly inspect your tank for cracks, holes, or gaps. You should also check the sealant around the base of the tank for any signs of deterioration.

When Should I Buy a New Tank?

If you’ve purchased a high-quality fish tank made from glass, it should last between 15 and 20 years. However, if you purchased a cheap variety, it could start to break down within 3 to 5 years. If you notice irreparable damage, it’s best to invest in a higher-quality model.

A Final Recap

Fish tank leaks are not uncommon, and they can be caused by several different factors, such as cracks in the glass, a faulty sealant, or a broken aquarium stand. In most cases, you can fix the problem by resealing the tank or replacing the filter. However, if your tank is severely damaged or quite old, it may be easier to replace it rather than risk further damage down the line.

About the author

Hey! I'm Antonio!

Betta fish keeper for over 6 years now! Since owning a betta I've also housed all kinds of tropical fish, and have seen all manner of problems and how to look after them!

If you need any advice you can always message me or better yet join the Facebook group where a community can answer your questions!