Aqualife Beauty

Aquatic Life Beauty

Aqualife Beauty Uncategorized How to seal a fish tank leak: Step by step guide for aquarium glass repair

How to seal a fish tank leak: Step by step guide for aquarium glass repair

As an aquarist, can you confidently and comfortably handle all/any eventualities relating to your aquarium? I guess you must be good at the tank’s contents care, but do you know what you’d do if your aquarium cracked? Do you even know how to tell if your fish tank is leaking? Well, it’s time you learnt that and also how to seal a fish tank leak if you don’t. It would be a great addition to your aquarium management and maintenance skills.

Even with good care for aquarium leak prevention, don’t be surprised to notice wetness on the floor beneath it. Most likely, the wetness is as a result of unnoticeable leak probably from a hairline crack in the fish tank.

How to seal a fish tank leak

However, the leak could also be caused by the wearing out of the aquarium’s sealant. The failure of the sealant may also be traced back to the manufacturer. Following that therefore, when the sealant holding the panes together turns bad (usually over time) or is defective, leaking is inevitable.

As you read on, you’ll know how cracks in aquarium glass come about as well as how you can do timely aquarium glass repair. That is however preceded by first knowing how to trace the leak in the fish tank.

That said, I assure you that fixing a cracked aquarium glass is not too complex. You can do it on your own. If you read through this guide and get yourself an aquarium glass repair kit, it is an easy DIY exercise.

Reasons why fish tanks crack:

Can aquarium glass break without human intervention? The simple answer is yes. This is mostly if it’s placed on un-leveled surface. It’s the top cause for aquarium glass breaking. The surface on which it sits on MUST not only be sturdy but also very even.

The flattening of the surface is critical so that the aquarium isn’t wobbling. In addition, all the 4 corners of your tank’s bottom should make contact with the surface.

Another possible cause is inherent defects traced back to tank’s manufacturing stage. To avoid this, you’d better source your aquarium from reputable manufacturers. This will nearly 100% save you the risk of buying a defective tank.

Further, impact from rocks and decorations placement at the bottom may particularly cause aquarium hairline cracks. It needs to be done gently and in a way that no movements are possible. The water column pressure will only make it worse and lengthen the crack. Urgent intervention is now critical.

How to find a leak in a fish tank for accurate fixing:

Knowing how to leak test aquarium is the next big test else you won’t solve the problem. One thing to note is that all leaks start from inward the tank. Following that therefore, resealing the aquarium has to be from inside. Any other way of your aquarium repair is at best an exercise in futility.

Below are possible means by which you can try to locate the leak;

  • Mark the tank’s water level once you note wetness. Thereafter, observe for any water decline for a while. Essentially, the leakage will stop right below leaking point.

However, this may not be the most reliable method especially if the leak is near the bottom of the tank. You risk losing too much of the tank waters. Besides, the water column pressure may exert a push on the leak area aggravating an already bad situation.

For a severe leak, it is a little easier to locate. A good checkup of the tank will easily be able pick out the spot. If lucky, the water could even be shooting a tiny stream through the seal.

  • If it’s difficult to finger out any suspicious point in particular, do a round the tank scans for wetness signs. Keenly observe any damp area. Dry the area and give it a look after a while. If the dampness still persists at the same point, there could be it. Those hairline aquarium cracks under water column pressure can allow water to sip through.
  • You may also check for any sealant peeling off or curling up. This is particularly so with the edges. It can be an area of concern.
  • Now, perhaps the quickest, most common and more accurate method is wrapping a paper towel round the tank. Wetness on the paper will automatically show at the leaking spot.

Having accurately identified the leak, it’s now time to sort it.

How to seal a fish tank leak:

First, fish aquarium glass repair can never be considered 100% fail proof. Moreover, some aquarium cracks are not worth attempting to repair.  Just have a complete glass replacement or better still, get a new tank.

Now, depending on the location of the crack/leak, you may either empty the tank or do the sealing with water still in it.  

How to fix a leaking fish tank without draining it:

To start with, this is possible with pinhole sized leaks but not with major leaks. It’s just not possible. You won’t do a good job.

In addition, if the leak or crack is again too low, then you unfortunately just have to drain the tank.

The steps here below will systematically guide on how to fix a leaking aquarium without draining it:

Make the leaking spot reachable:

The first and obvious step to sealing a fish tank leak is to ensure the leaking spot is accessible. It shouldn’t be under water. Therefore, depending on the location, you may have to scoop out some water.

For that, you will need a clean container to temporarily hold the water drawn. This container should not have traces of detergents. This is because they’ll kill the bacteria in the water as well as unsettle the water’s natural chemical balance.

It is in this container that you should now evacuate the fish into as you work.

Scrap off the old the sealant:

The leak at that spot is because the sealant has weakened and turned bad. You therefore have to remove it. To scrape it off, use a razor blade. The razor will not leave scratches on your glass and will ease the scraping.

Caution however is that you be careful to only remove the silicone just around the crack.

Be careful too that the sealant you are scrapping off doesn’t fall into the water.

In addition, don’t touch the sealant between the glass panes.

And just so you know, old and new sealants don’t bond well. Therefore, before you apply the silicone for aquarium repair, the old one should be fully scrapped. That is the only way to get perfect results by the new sealant.

Cleaning the leaky spot:

If you don’t want the frustrations of repeat jobs, then you have to properly clean the surface to be sealed. Just like on old sealant, the silicone used for fish tanks repair equally won’t properly stick on dirt.

Well, dampen a clean towel with acetone and gently wipe the area clean. It is no different with what you do when cleaning off algae in on the tank.

However, be careful not to apply too much pressure lest you worsen the situation.

When you are sure it’s well cleaned, you can use a paper towel to wipe of the dampness left by the acetone. However, you may still choose to leave it to air dry.  A 15 – 20 minutes wait is sufficient for the place to be completely dry.

Seal the leak:

It’s now time to seal that leak with a good fish tank sealant. However, this is only after you are satisfied the spot is well cleaned and dry. While there are many aquarium silicone sealants out there, only use safe fish tank repair silicone. That sealant MUST be 100% silicone and non-toxic. In addition, it MUST not have fungicide properties. Moreover, it should be a high Modulus product.

If the silicone used to repair the tank isn’t as described above, you will be exposing the tank water and the fish to poisoning.

A caulking gun will do a good job of applying the silicone on the surface being repaired. Further, to smoothen the sealant over the spot, use a caulking tool. A damped finger can also smoothen it out too; the choice is yours. Don’t stop till there is silicone sticking out else fish will be nibbling on it soon.

Well, you may be tempted to seal the leak from outside; just don’t do it. That is not how to seal a fish tank leak. It doesn’t matter whether if you are repairing a small leak.

The guarantee with the sealant from the inside is that, the water column will be pressing on it. Subsequently, the pressure therefrom will make the sealant hold and seal even better.

Allow time to dry:

For the silicone applied to dry fully, it needs at least 24 hours. Adding the water back before the seal is well dried will only mess it up. The water effect softens up the silicone which will subsequently make it peel away.

Observe the spot for leakage:

After the sealant has fully dried, you can now add water. Make sure the water level is slightly above the spot you’ve just sealed and observe for any leaks. You can thereafter increase the water volume gradually.

This ensures you are building water column pressure slowly. Besides, you can still place a paper towel on the outside of the sealed spot.

If no water level drop or wetness on the paper, you can be sure the sealing was successful. However, if that’s not the case, you have no choice but to start the process all over again. Well, you can involve a professional to do it, but why while you can learn from that?

Put back the aquarium as before:

Now that you not only know how to seal a fish tank leak but have done it successfully, it’s time to put back the tank as before.

Safely get the fish and the decorations back in place.

I guess how to fix a leaking aquarium without draining was that easy; or was it?

How to fix a cracked aquarium bottom/side:

Just as with sealing a fish tank leak, fixing a crack aquarium isn’t too complex either. This however is dependent on the extent of the crack and its location too.

However, fixing a broken side glass may not be too effective. This is because the water column pressure will push on it and soon enough, it will come undone. Besides, the glass patch will water down the good look of the aquarium’s face.

This is not the case though if the crack is at the bottom. First, the support from the aquarium stand from below holds the glass in place. Second, the substrate and the water pressure will sit on the patch.

The force is matched and counter balanced by the support beneath. Most important, remember that the surface must be 100% level besides being sturdy.

The following steps will guide you to doing just that. They are nearly a replica to those of sealing a fish tank leak.

Empty the tank:

In this case, you can’t seal this fish tank with water in it. Therefore, you’ll have to have alternative clean containers to move the tank’s content as you repair it.

  • Start by moving half of the water into one tank. Into this, move the fish.
  • To the second, drain the remaining water. Further, move the tanks decorations, plants and all appliances; say heater, filters et al.

Caution is that you should do it in a gentle way. The already very fragile tank needs handling with extra care. Most importantly, you should avoid exerting unnecessary pressure particularly around the crack.

Clean and dry the area:

With a clean towel, wipe the tank dry. For the cracked area, you’ll not only dry but first clean to remove any dirt. For that, you may need to use white vinegar to clean that part especially if there is grime build-up around it.

Clean thoroughly but gently lest you exert pressure that will widen the crack.

You should equally clean the glass to be used for patching the crack. FYI, the most ideal repair glass should have a thickness of at least 6mm. Besides, it should be able to spread out about 3” on both sides of the crack.

Let them to fully dry.

Apply silicone:

You must get the right silicone for fish tanks repair for the safety of your tank ecosystem. It must have the safety attributes discussed earlier here above. In addition, the silicone must be specific for aquatic conditions. There are many in the market.

You want to seal that fish tank leak; use the right and safe materials.

You will have to sufficiently and thinly spread it over the area and about 3 inches on each side of the hairline crack.

“Mend” the crack:

Now, position the tank in its best leveled and sturdy surface. Thereafter, slowly and carefully lay the patching glass on the area observing the 3” inches on both sides. Gently apply pressure so that it sticks firmly.

Give the “patch” time to dry before testing with water. 20 -24 hours will be enough time for the silicone to fully cure.

You can observe it for a few more hours before restoring everything in the tank.

CAVEAT: This aquarium glass repair is ideal for sizable cracks. For extensive cracks, a full fish tank glass replacement is most ideal.


While you may know how to seal a fish tank leak, it also important to know what leaks and cracks are worth fixing attempts.

If however you take exceptional care of your tank, you may not have such problems for a long time. Well, that is if we rule out defects from the manufacturer.

Leave a Reply

Your email address will not be published. Required fields are marked *

%d bloggers like this: