7 Reasons Why Fish Tank Cracks (+How To Fix It!)

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Did your fish tank crack just now? And you want to figure out the reasons behind it. Also, the solution and preventive measures, so that it never happens again? Then you are in the right place.

Here’s Why Fish Tank Cracks:

  1. The surface of the fish tank is not leveled.
  2. The quality of the fish tank glass is bad.
  3. Due to the falling of heavy rocks.
  4. Using the cleaning tools carelessly.
  5. Something stuck under the fish tank.
  6. The temperature difference between the glass and water.
  7. The temperature difference between the glass and the surrounding.

Recently my 23-gallon tank cracked and so I know actually how it feels when such happens. And, in this article, I’m going to share whatever I learned so far along with my experience. Stick with me till the end!

You can also watch this video from my YouTube channel eFishkeeping:

Here are the 7 reasons why fish tank cracks explained in detail:

#1. Surface Of The Tank Is Not Leveled

This is one of the most common and primary reasons why many fish tank cracks.

The weight of a fish tank increases when we add water to it. There will be no issue if the surface where you kept the fish tank is leveled properly.

But if there is even slight unevenness in some particular area of the surface then the water pressure difference will start building in that area.

Even if you don’t notice something in the initial days of setting up the tank. Eventually, after a few days that slight pressure can cause a crack in the glass and hence leakage.

The best thing you need to do after you set up your fish tank is to rock the tank slightly to check if the stand is sturdy enough.

If you feel the leg rock of the fish tank stand, then just fix it by putting something in the gap. To be more assured you can also use a ‘spirit level‘ to see if the tank water is leveled properly or not.

CRAFTSMAN Torpedo Level, 9 Inch, With Shock Absorbing End Caps

Get it here! (on Amazon)

So if you make sure that the tank is completely leveled then more than half of your problem is solved.

My experience:

I did a setup a fish tank recently at our home with my Dad. Everything was just fine but then after 4-5 days in the morning when I woke up half of the tank was empty.

There was a 4-inch small crack on the bottom of the aquarium. Whether the crack was inside or outside, I wasn’t able to figure it out at first (since this situation was new to me).

I was a little tensed and immediately drained the tank and shifted all the fish in a separate tank. Then started my research (guess you are also doing the same right now). After doing it I applied the knowledge and was able to fix my fish tank very easily.

But I was thinking what caused the problem and then I realized that the point from where the tank cracked, underneath I had placed a sheet of plywood improperly.

So I did proper padding in that area and also used foam sheets. And sealed the area with a silicone gel which I have discussed ahead.

#2. Bad Quality Fish Tank Glass

Another reason why fish tank may crack is the quality of the fish tank is quite bad. If the silicone is not used properly to join the glass slides while making the aquarium then chances of leaking will increase.

And not just leaking, if the silicone is not used properly to seal the corners properly then due to pressure the tank might even explode.

So make sure that the place from where you are buying the aquarium is trustworthy. You can find some quality fish tanks here on Amazon.

#3. Heavy Aquarium Rocks Placed Carelessly

Often if you place very heavy stones or gravels improperly then also it might create some problems. Most of the fish tanks are glass so if while doing the fish tank set up if you place a heavy stone hardly inside then it is obvious to develop a crack.

So make sure while you are placing the aquarium decorations, stones, gravels, and all that stuff. Especially with the heavy ones.

Also, one important point to remember is never ever to move your tank from one place to another when it is filled completely with water and fish.

#4. Using Cleaning Tools Carelessly

If you are using the cleaning tools to scrape of the dirt from the fish tank glass then okay, no issue but be careful that you are not using it so hard that can cause slight hairline cracks.

Especially when you using it on the edges of the tank you need to make sure that the silicone doesn’t come out while doing it. Otherwise chances of your aquarium leak will increase.

Read Related: Is It OK To Use Vinegar In Aquarium With Silicone Seal?

#5. Something Stuck Under The Fish Tank

This happens to me. When I take away the fish tank from its stand (for cleaning or any other issue) and again place it, I notice that some aquarium gravels are still trapped underneath.

If your attention is elsewhere while doing the setup or cleaning then this kind of small mistake happens. And since the small stones are not easily seen you forget to take them away.

Now I already discussed with you how an uneven surface causes pressure difference inside the tank which ultimately develops a crack. Hence be sure that there is nothing on the surface before placing your tank on it.

Also Read My Article: Can Fish Tanks Be Kept Near Windows? (Explained)

#6. Temperature Difference Between Glass and Water

Unlike other reasons the aquarium cracking due to temperature difference is highly unlikely unless you doing some science experiment with your tank.

If you are pouring hot water in your tank which is cold abruptly and vise versa then obviously the tank will crack. This is the molecular property of the glass, right?

#7. Temperature Difference Between Glass And Surrounding

Similarly, if you keep your tank in an area that is quite cold while the fish tank water is regulated and hot enough (because you have a heater for fish).

Then again the temperature difference will be created and cause cracks in the tank. Hence if you live in extremely cold conditions then make sure that your fish tank is kept in a temperature-controlled room.

How To Fix A Cracked Aquarium?

If there is a hairline crack of 2-3 inches then just apply the silicone gel on the cracked area front and back, and leave it to dry for 24 hours. But if the crack is bigger, then attach one extra glass piece to the cracked area for better protection.

You can use any silicone gel as a sealant but make sure that it is not harmful to the aquarium fish. Here’s a silicone sealant by Aqueon which is specially made for aquariums.

Aqueon Silicone Sealant Clear 3 Ounces

Get it here! (on Amazon)

Now if you want a video demonstration of how to fix a crack in an aquarium then you can watch this video by Fine Fins.

How To Prevent Aquarium Breaking?

Here are the key to remember in order to prevent aquarium breaking:

  • Make sure that the aquarium surface is completely flat.
  • Place the heavy aquarium stones and decorations gently inside the tank.
  • Do not move your tank when it is filled with water and fish.
  • Buy your aquarium from a trusted place and make sure that the quality is good.
  • Don’t add warm water in a cold water tank or vice versa abruptly.


So that’s it! Hope you liked reading this article. Please do share this with others if you found this helpful. Thanks and Happy Fishkeeping!

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Related Questions:

What Are The Chances Of Fish Tank Breaking?

Less often, but a fish tank can crack if the surface is not flat. Some fishkeepers experience this issue, especially beginners. Although most of the time the crack is like a slight hairline at the bottom or on the side which can be fixed easily if looked at proper time.

How Often Do Fish Tanks Explode?

Very rare! But if the manufacturing of the fish tank is quite poor, or if the surface of the fish tank is not leveled then cracks might occur which if overlooked might even lead to the tank explosion.

What Happens If Aquarium Glass Break?

If the aquarium glass break is minimal then it can be repaired. But if the damage is more then there is no other choice other than to replace it with a new aquarium.