How to Fix a Crack in a Plastic Fish Tank: Step-By-Step Guide

Owning a cracked fish tank is not particularly helpful. Acrylic fish tanks are costly, and buying a new one or taking it to be repaired will only increase the price. Luckily, it is an easy DIY project as long as you own the proper tools and can follow instructions. 

How do you fix a crack in a plastic fish tank? 

  1. Collect all your supplies.
  2. Remove all the contents from the tank and thoroughly wash it out.
  3. Take a small drill and drill a hole until it meets the end of the crack. 
  4. Fill a precision tip applicator bottle with the acrylic cement and fill in the hole, which will then run into the crack. Apply acrylic strips inside the tank if desired.
  5. Place the fish tank on its side and apply enough pressure to push the crack together. 
  6. Use a heavy object to keep the crack together while it sits overnight.
  7. Test your Tank if needed         

Cracks and scratches often happen to fish tanks. If you’re new to the world of fish and aquarium maintenance, this article will try to teach you all the necessary steps to fixing and maintaining your tank. 

Our Step by Step Guide to Fixing a Crack in a Plastic Fish Tank

Follow the guidelines closely to learn all the necessary steps to patching up a crack in your fish tank safely and effectively. Let us begin. 

  1. Collect Your Equipment 

For this DIY project, you will need:

  • Acrylic Plastic Cement 
  • Water Hose
  • Precision Tip Applicator Bottle/ Syringe 
  • Face Mask
  • Gloves 
  • Towel 
  • Small drill
  • Square acrylic strips
  • A can-do attitude

To pick the best materials, let’s understand a bit more about each one:

Acrylic Plastic Cement

Acrylic plastic cement is a bonding agent that works to attach acrylic too, you guessed it, acrylic. It will first soften the plastic surface and then weld it together. 

Once the cement sits for a few days, it is safe for your pet. For a small and shallow crack, you’ll need a diluted cement which is easy to use and dries quickly; deeper and broader cracks will require a thicker bonding agent.    

A well-known brand used on aquarium tanks is called Weld-On (Amazon link), but feel free to research other brands in the nearby store. 

There are two different types of cement to choose from:



Usually, any cement over Weld-On #16 will be unnecessary for a simple project like this. First, try using a thin cement and if it doesn’t move on to a stronger bonding agent. 

Do not use a silicone-based sealant. Silicone will only work on glass aquariums. Acrylic must be bonded together, which can only be achieved through the acrylic cement.

Water Hose

Use a water hose to thoroughly rinse out any leftover gravel, sand, and built-up dirt. Oh, and of course, take your fish out of their tank first, or suffer the consequences.

Precision Tip Applicator Bottle/Syringe

An applicator bottle is a small bottle with a long fine tip at the end. Using a fine tip, either from a syringe or a precision bottle (Amazon link) will allow you better accuracy and control over the cement. 

Face Mask/ Gloves

Wear a face mask and gloves when you begin working with the cement. The fumes are toxic, and the cement irritates the skin. Working on the fish tank outside is also recommended. Remember, safety first. 


If your precision bottle tip or syringe can not reach directly into the crack, you will need to drill a small hole at the end of the crack. You will want the smallest drill bit available, which is one-sixteenth. 

Acrylic Strips

It’s handy to own a few strips of plastic for backup. You won’t need to go overboard on the size and width of your spare acrylic strips. If you have a major crack on your hands, it’s best to buy a new tank.

A Can-Do Attitude becomes Done

Just a side note. Stay positive while you’re working on this project. It can be quite tedious and frustrating. If you hit any problems, be patient and don’t beat yourself up over any mistakes.

1. Clean and Prepare your Tank

Empty your tank of all fish, plants, gravel, and sand. If necessary, go outside and use a hose to wash out any built-up dirt and residue. Your tank must be clean.  

After a thorough wash, wipe it all down with a towel and then let it air dry. Once your fish tank glimmers in the sunlight, you’re ready to begin the project.

Pro Tip: Wiping out your fish tank with a microfiber towel will prevent the acrylic from being scratched. 

Set up your workstation with plastic or a newspaper to cover and protect your floor or table.

2. Using a Power Drill

Yes, it’s power tool time! Using a small drill will only be necessary if you’re unable to fill in the crack with the syringe directly. Use a drill with a one-sixteenth bit. Calmly and slowly drill a hole at the end of the crack. Only drill deep enough to meet the end of the crack. Do not drill deeper than the crack.

3. Acrylic Cement Solution

Wear a facemask to avoid breathing in the fumes and wear gloves when you work with the cement.

If you drilled a hole: 

  • Use a thin acrylic cement solution 
  • Use your syringe or precision tip bottle to fill in the hole slowly. 
  • Watch to make sure the cement is running into the crack. 

If you did not drill a hole:

  • Decide which cement to use. the larger and deeper the crack, the thicker and stronger the solution  
  • Use your syringe or precision bottle and directly apply the solution to the crack.

Keep in mind that the acrylic cement is a heavy-duty bonding agent. It will melt any part of the tank it touches.    

4. Acrylic Strips

This is an optional step. Use a thick cement to attach a small strip of acrylic over the crack on the inside of your tank. You still need to add cement to the outside, but this can provide additional strength. If your square is not quite the right shape, take a heat gun to bend the strip.

Securing the Crack

Allow the cement to sit for a minute to work its magic and then apply pressure to the tank so that you push the crack together. Rest a heavy object, like a dictionary or large bag of rice, on your tank and let it sit for a day or two. Badabing badaboom! Leaks are gone.

Test Out Your Tank 

Once you’ve finished the steps above, it’s time to try out the tank. Fill your tank up with water and check for any leaks. Leave the water in for a couple of hours to make sure the crack is truly sealed. If your tank is still unfixable, it’s time to switch it out for a new one, but which type?

Which is Better: A Glass or Acrylic Fish Tank?

After reading through all the instructions, you may be rethinking your acrylic tank. Never fear, here is a comparison of plastic and glass aquariums.    

Acrylic Fish Tanks 

Acrylic, also known by the alias plexiglass, is a type of transparent thermoplastic specifically designed to be lightweight and durable. The best attributes of these tanks are:

  • Lightweight
  • Customizable shape
  • Durability


Acrylic fish tanks are lighter than glass. Plastic tanks don’t need to be as thick as glass tanks to support the same amount of water. If you are interested in owning a small fish tank, an acrylic tank is an excellent choice because it will be easier to move around. 

A glass tank can easily weigh up to 10x more than an acrylic fish tank.


Acrylic is a flexible plastic that can be molded into almost any custom shape imaginable. If you want a custom made fish tank, acrylic is your best choice.

Acrylic is also superior because plastic doesn’t “bend light” as much as glass tanks. This means the light that enters through a plastic tank will not distort the images of the tank. When light passes through a glass tank, it distorts the fish because the light has been refracted four times through:  

  • Air
  • Glass
  • Water 
  • Fish

Then it is reflected out of the tank.   


Acrylic tanks are the clear winner in this department. Acrylic tanks are less prone to chipping and cracking and are far more durable against collisions. Although they are incredibly durable, we don’t recommend finding out your tank’s impact resistance through the first-hand experience. The easiest way to never test your tank’s durability is to follow these steps: 

  1. Don’t drop it.
  2. Don’t bump it.
  3. Set it on even surfaces.

Another positive factor is that acrylic is an adaptable material. If you’re looking to modify your fish tank, choose a plastic tank because you can easily drill into it. This is why fixing the crack yourself is doable only on a plastic fish tank. Don’t fix a crack in your glass fish tank unless you are experienced. Glass is not a forgiving material. 

Heat Retention of Acrylic Fish Tank

Acrylic tanks provide better insulation which allows them to trap heat longer than glass tanks. This isn’t a huge factor if you’re keeping cold-water fish, but it’s important to keep in mind if you own tropical fish. 

Acrylic tanks can retain up to 20% more heat than the glass tanks, which means less expensive electric bills!  

Acrylic Fish Tank Cons

Here are a few of the less desirable qualities of an acrylic fish tank:


Acrylic tanks are far more expensive than their glass alternatives. Even though acrylic as a material is cheaper to manufacture, acrylic tanks still take the cake when it comes to high prices.  

There is a simple answer: Glass tanks, although a more expensive material is simpler to manufacture. They require less specialized tools and are easier to ship. Why is glass easier to ship if it has a lower impact resistance? This brings us to our next con.


Acrylic tanks are scratch-prone and even a slight brush against the tank with a hard object will do the trick. If you plan on having many kids around or keeping the tank in a high trafficked zone, we would steer you away from an acrylic tank as it is much more likely to get scratched.

This little problematic flaw is why shipping plastic tanks are more expensive than glass tanks that don’t scratch. While it may be less expensive to produce plastic, it’s another story when a shipment of plastic fish tanks are sent back because they’re un-sellable. Sadly, this also means cleaning a plastic fish tank is far more time consuming than the glass counterpart. 

Base Support

Acrylic tanks have the advantage of weighing less, but its flexibility requires the tank to have a full bottom support stand. If there isn’t full support, the bottom will collapse. Glass tanks are heavier and denser, which means they only need to be supported on the outer edges of the aquarium, which allows you to have a smaller base. If you own a large tank, it’s best to have full bottom support for both types of tanks. 


Clarity is a top priority if you are interested in looking at your fish. Glass doesn’t lose its clarity over time, UV light doesn’t degrade it the same way it breaks down acrylic. Although it will take years, all acrylic tanks become sun damaged which makes the plastic turn yellow and brittle. There are in fact “UV- resistant” plastic aquariums, but they still do not compare to glass aquariums in clarity.   

Worst Case Scenario: The Crack Expands To…

Yes, the nightmare we fish owners fear above all else: An exploding or leaking fish tank. The moment instant chaos ensues as your floor is littered with plants, gravel, and tropical fish flopping all over the room.

Then to make matters worse your CAT speeds through the room with a wild look in its eyes you’ve never witnessed before. Let’s identify the reasons why tanks crack so we can prevent the example above. 

Why Did My Plastic Fish Tank Crack?

There are two main reasons why your tank can crack: 

  1. Poor manufacturing
  2. An unlevel base

There is little we can do about a poorly built fish tank. The only thing we can control is who and where we buy our fish tank from. Always purchase a fish tank from a trusted store or person. If possible, take the fish tank out of the packaging before purchasing to check it for scratches or cracks, then make sure it is fully repackaged for transportation home.  

An un-level base is the most common issue that can be easily rectified. If the aquarium is held up by an uneven base, the weight from the water will add pressure to the lowest part of the tank. 

It is also important to keep your fish tank out of direct sunlight because it will eventually damage the plastic. This will greatly prolong the lifespan of your tank. Check your fish tank for any leaks once a month, this will alert you to any future problems.

Maintaining Your Fish Tank

Keeping your fish tank at optimum condition will increase the lifespan and happiness of your fish and your tank. Cleaning a plastic fish tank is similar to cleaning a glass tank, but it needs to be done slowly and carefully to avoid scratching the sides. The main point with acrylic tanks is to avoid scratches. 

Never clean the exterior of your plastic fish tank with:

  • Windex 
  • Ammonia
  • Alcohol 

Any abrasive chemical will damage the tank. You’ll need to buy cleaning products specifically designed for acrylic tanks. Change out a rough sponge and cloth for a microfiber cloth and magnetic cloth cleaning tool. Two cleaning products essential to your maintenance kit:

  1. A magnetic cloth tool
  2. A plastic scraper tool

You can only use the tool specifically designed for a plexiglass fish tank. A magnetic cleaning cloth is your best option because you can leave it on the glass tank and regularly rub off algae build up. 

If there is build-up at the bottom of the tank, gently push away any gravel and use a plastic scraper tool. You can either buy a scraper specifically made for an acrylic tank, or that pesky plastic gym membership card you never use. To each their own. 

A sand or gravel vacuum is a superb addition to your cleaning routine as long as you’re careful not to bump into the tank. I believe the main takeaway is to clean your tank – carefully. Of course, minor scratches are inevitable. Fortunately, you can purchase an acrylic scratch removal kit which will easily remove minor scratches.    

What Did We Learn?

In conclusion, choosing the correct tank depends on what you’re looking for. Both glass and acrylic tanks have their pros and cons. I would recommend visiting a pet store to voice your concerns and dreams to a professional. But, if you choose an acrylic tank, you now have the confidence to fix a crack and how to keep it from cracking in the future.

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