How to Reseal a Fish Tank? Explained Step-by-Step

Owning a fish tank brings many responsibilities with it.

In addition to taking care of their fish and other aquatic life, owners will need to ensure that their aquarium is kept in good condition.

One of the most concerning issues that could happen to your fish tank over time is leaks.

If there is any leaking, you may need to reseal the fish tank.

This process involves many steps, such as cleaning, removing the old sealant, applying new sealant, letting it dry, and testing the repaired tank.

However, this process needs to be performed with care and precision.

Keep reading to learn about the precautions you need to take when resealing your fish tank.

What Causes Fish Tank Leaks?

Most fish tank leaks are caused by a failure in the sealant holding the glass panels together.

This flaw could arise during the tank’s initial construction, or it could appear over time as the sealant weakens and peels away from the glass.

Some tank owners inadvertently damage the sealant by using algae scrapers close to the tank’s edges.

How to Identify a Leaky Fish Tank

Whether you have just purchased a new fish tank or own an existing one, it’s important to keep an eye out for any signs of leakage.

If you are taking an old tank out of storage, you can check it for leaks using the following process:

Visually Inspect the Empty Tank

The first step is to look over your tank carefully and identify any visible cracks on the surface of the glass.

See if you can spot any chips in the areas where the glass panels connect.

Some older or damaged tanks have circular chips close around this region.

These blemishes don’t just look unattractive, but they could also develop into leaky spots over time.

Check the Silicone

Fish tank leaks usually occur around silicone sealant between the glass panes. You can check for a compromised seal by feeling around the silicone and looking for any portions that are lifting off the glass.

The sealant that is still functional should feel sticky or “gummy”, which means it has still retained its adhesive properties.

If your silicone feels hard, it could crack or develop a leaky seam over time.

Fill Up the Tank

The simplest way to check your tank for any leaks is to fill it with water. However, you should avoid doing this indoors, as any leaks could flood the room.

You can also attempt this in a shower cubicle or in a basement close to a drain.

It’s also important to ensure that your tank is level before filling it with water. Keeping your aquarium tilted at an angle puts extra water weight on the connecting seams, which could cause them to pop.

You can use a level instrument to check if your tank is resting on a horizontal surface.

Once these checks have been completed, you can start adding water to the tank. Begin by filling a couple of inches of water and allowing it to sit for a few minutes.

Look For Signs Of Leakage

Check for any spots around the seams where the water could be beading.

Some leaks tend to be very slow, and can only be identified as beads of water on the silicone’s external surface.

If things look good so far, you can add a few more inches of water to the tank. Repeat the aforementioned process until you spot signs of leakage.

If the tank appears to be leak-free during this initial check, you should let it sit for 24 hours. If no water appears to have escaped by then, your tank should be safe to use.

However, if any leaks have occurred, you will need to empty your tank as quickly as possible using a bucket.

How To Reseal A Fish Tank

The process for resealing a fish tank is given below.

Clean Your Tank

Before starting the resealing process, you should clean your tank using a glass cleaner and paper towels.

Be sure to get any grime or algae off the glass surfaces so they are perfectly smooth and shiny.

Remove the Old Sealant

You should then start the process of removing the old sealant from the tank’s corners. Use a utility knife to pierce through the silicone and scrape it off the sides of the glass.

This process should be repeated along on all sides of your tank.

You can use tweezers or pliers to get rid of any sealant that remains in the corners of your tank.

Use Masking Tape

The next step is to apply masking tape near the corners of the tank.

This tape should be stuck parallel to the vertical joints, but approximately ¼ inch away from the corners themselves.

This step ensures that the sealant’s edges follow a straight line after it is applied.

Apply the Sealant

Once your masking tape is in place, you can start applying your sealant. You can use any aquarium silicone sealant for this purpose as long as it is fish-safe.

Start by depositing a line of sealant in the corner of your tank, and work your way upwards.

You don’t have to use a large amount of sealant, but do make sure that there are no exposed gaps or narrow points in your sealant line.

You can then use your finger to flatten and even out the silicone so that it covers each inch of the joint nicely.

Remove The Masking Tape

Once you’re confident that you’ve applied a decent-sized layer of silicone, you can start to remove your masking tape.

Be careful not to disrupt the fresh layer of sealant during this step.

The tape should be removed immediately to stop the silicone from setting on it. Attempting to remove it after the sealant has set could create gaps.

Let The Sealant Dry

The next step is to sit back and wait for the silicone to dry.

This process could take between 24 and 48 hours. Avoid filling your tank with water during this time, as it could undo all the work you’ve done.

Test Aquarium Tank for Leakages

The final step is to check your tank for leaks. You can use the leak checking method mentioned earlier in this guide for this purpose.

If everything has worked out correctly, your fish tank should be ready to use again.

How Much Does It Cost To Reseal A Fish Tank?

If you reseal your tank yourself, the whole process shouldn’t cost more than $20.

Assuming you already own a utility knife and household glass cleaner, you will need to purchase only the silicone sealant and masking tape.

This process is much cheaper than purchasing a brand new tank, which could set you back hundreds of dollars.

Why You Shouldn’T Use A Leaky Fish Tank

Many tank owners tend to neglect minor leaks that don’t cause significant spillage.

They may believe that a few beads of water escaping through the sealant shouldn’t be cause for concern.

However, a tiny leak could suddenly turn into a large one that could flood your room. This could be especially problematic if it occurs overnight.

Neglecting any leaks in your tank could endanger the lives of your fish, so it’s important to address a leak as soon as it appears.

How Hard Is It To Reseal Your Tank?

Resealing your fish tank is a bit more challenging than most people realize. The silicone used for sealing your tank does a great job once it is properly applied.

However, fresh silicone does not bond well with the old silicone sealant on your tank.

If the existing sealant has a tiny leak, dabbing some new silicone on the same spot won’t do much good.

This is because the water pressure can force its way through the gap between the two sealant layers.

Owners that wish to reseal their tank will have to remove 100% of the existing silicone before applying a new layer.

If you aren’t confident about your ability to perform the resealing process correctly, you should ask a professional to do it for you instead.

Alternatively, you could just purchase a new fish tank.


Resealing a leaky fish tank can be a tricky process if you have never attempted it before.

Once you have established that your tank has a leak, you will need to drain it and allow it to dry.

The tank should then be cleaned using a glass cleaner. You must then remove all the old sealants using a utility knife.

Once all the sealant residue has been removed, you should apply masking tape along the joint edges.

Apply a layer of aquarium silicone sealant in the corners of the tank and flatten it out using your fingers.

Then remove the tape and allow the sealant to dry for 24 to 48 hours.

You should then test your tank for leaks before filling it up and adding your fish back in.

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