Leaky Aquarium: Causes, Fixes And Preventions

There are very few sights in your own household that can induce a moment of panic, of sheer disbelief, like a puddle of water beneath your aquarium.

Immediately questions race through your mind from what’s happened to my aquarium? where is the water coming from? and the ultimate question that blares in your mind like a klaxon, as the inhabitants in the aquarium glare at you accusingly, is: what do I do now?

The rate at which the water is leaking is going to be a decisive factor in how urgently a solution has to be found, and how quickly you will have to act.

After this moment of dread eases, and you start to believe that things can’t get any worse, you notice that the wet patch beneath your prized possession is actually spreading, that it was bigger than it was a moment ago. What to do?

A lot of your options will depend on where the water is leaking from, is it a possible joint seal failure or is there an actual crack in the aquarium?

Whichever it is, a solution has to be found quickly or the slightly panicked look on the faces of the tank’s inhabitants are only going to get worse.

Once this impending catastrophe occurs, is there a solution?

What Would Cause A Fish Tank to Leak?

There a several reasons why an aquarium would seemingly start to leak without reason. Seemingly is the right word because one of the possible causes of water seepage could be at the point of manufacture, and could have been lurking in the depths of the tank to happen at an inopportune moment.

In this case, it’s important to remember and consider how a tank is actually manufactured, irrespective if the material utilized is glass or acrylic.

A typical aquarium has 5 pieces of glass, four sides, and a base. The thickness can range from 1/4 thickness (six millimeters), and increase from there depending on the tank size. But that increase in thickness can be mitigated on larger tanks by using a glass brace to add support otherwise the weight and thickness of the glass would be incredible.

Now, presuming that there are no defects in the glass itself the point of weakness would lie elsewhere, and the first point of a possible failure is going to be one or more of the joints.

Silicone is used to create the seal on the joints but if a seal is not applied correctly at the time of construction, minuscule air pockets can be left unnoticed, creating weak focal points.

The quality of the silicone can also be a factor, possibly peeling away unnoticeably from the surface of the glass, slowly leaving a lurking flaw that could expand over time until bursting at the seam.

The combination of these pinhole-sized flaws and a sub-standard or inadequate seal is the most common point of failure over time, but glass cracks and breakages actually occur a lot more often than you might imagine.

This specific type of breakage can lead to a major leak but is not normally a fault instigated at the point of manufacture but caused by common human interaction.

People love fish, and one of the reasons for having fish is that you want to see them when you want to see them.

Sometimes they are hidden under plants or just on the other side of the tank, doing their own fishy things away from prying eyes.

So, the typical reaction for getting their attention, for getting them to swim towards you, is to tap tap tap on the glass.

Children are some of the main culprits but adults are at fault here, too. The problem occurs either when the strength of the taps are harder than anticipated or an accumulative effect mounts up until an infinitesimal chip occurs, which morphs into an unnoticeable crack, which grows into a very noticeable streak and then into a worrying leak.

A crack in the glass has the potential to be the most daunting of leaks because the water inside the aquarium is adding extra pressure on a constant basis. If left unchecked, unnoticed or unresolved it can quickly become a major headache that could involve a complete tank drain and transposing all of the unhappy inhabitants to temporary alternative accommodation until the problem is resolved.

A third, and sometimes overlooked source of the dwindling level of water in an aquarium, could simply be a water pump. If the pump doesn’t have a non-return valve, for example, it has the potential to suck water out of the tank unnoticeably if there is a power failure. If that happens the pump can stop pumping water in and start sucking water out.

The airline that leads from the pump into the tank may be thin but if this occurs whatever amount of water that seeps into the pump will slowly fill it up, ruin it completely beyond repair, and then leak out of the air inlet point from the now defunct pump onto the floor.

So, the water pump is always worth checking.

Preventing A Tank From Leaking

Prevention is better than the cure is an old adage that rings true in many instances, and can avoid many future problems before they can occur.

When it comes to the lifespan of an aquarium, and specifically making it leakproof, everything starts with the glass.

At the first point of production the glass has to be washed, dried and cleaned to within an inch of its life. Acetone is used to eliminate all traces of the film of oil that coats all new glass for protection, and also to get rid of any spots of dust.

If this process isn’t carried out reverently and painstakingly then there is a possibility that the silicone will not adhere properly and seal like it should, leaving potential problems lurking in one of the corners.

At the point of joining the glass panels together, it is crucial that the correct silicone sealant is used. It has to be 100% nontoxic and be approved for use in aquariums. The last thing you’d want is for your very expensive tropical fish to be introduced into their new habitat and be served a nasty dose of poison from the toxic sealant seeping into the water.

Purchasing a brand-new aquarium is an indulgent treat and a pleasure to unwrap, but even if your first tank is going to be a used model or you have had a great deal at a sale, an initial water test is a must.

A manual inspection may give some clues as to the overall condition so run a finger around the seals and over the surfaces, checking for any dinks or uneven dips.

After that, if all is okay, place the aquarium on an even, level surface outside or in a garage where if there is a leak of any kind it will not cause irreparable damage to whatever lies beneath. Also, the type of water at this stage is unimportant as it will be thrown away after a few days.

Fill the first level of water to only about 1/4 of the aquarium and then let it sit for 24hrs; dry the outside at this stage so your eyes won’t be playing tricks on you later on.

Check for leaks then fill to the next mark for another 24hrs.

After that, fill to 3/4 full and then completely fill to your desired level, with 24hrs in between; the last fill can be left a day or so longer for peace of mind.

Leaving the aquarium slightly longer when it is completely full also acts as a stress test. Some used tanks have been known to have a blown panel, and if that weakened panel gives out unexpectedly it would result in a sudden deluge of water all over the floor mixed in with a lot of unhappy fish, to put it mildly.

Using this slow fill method allows you more time to actually locate any possible pinhole leaks and repair them before moving the aquarium into its new place and introducing the colorful array of fish to their new habitat.

It is highly recommended at this positioning stage that a spirit level is used to ensure that the aquarium is set squarely in place. If not, the water pressure will be distributed unevenly throughout the aquarium which will cause an unbalancing of water pressure.

This is often overlooked in the haste to start the next phase but if the aquarium is not housed correctly, slightly askew then an inordinate amount of pressure could build up at one particular stress point rather than being equally distributed throughout.

So once all the precautions and safety measures have been undertaken the aquarium is ready to be seated into its new showpiece position in your home. It is recommended to repeat the gradual water filling process at this stage. Just in case.

On a regular basis, whether weekly or monthly, it is advised just to check on the quality of the silicone sealants on each joint. Sometimes the silicone can degrade, a slight strip of it can peel away or a fish could be nipping surreptitiously at it whenever your back is turned. You never know.

Checking on the state of it every so often enforces peace of mind and if there is a problem you can catch it very early on or, at the very least, you’ll be aware of the situation and have it on your to do list.

It’s better to spend a minute or two now, to have peace of mind, and not to waste hours at a later date because something went unnoticed.

Fixing A Leaking Fish Tank

The source of the leak has to be located before a repair can be started and, believe it or not, a leak is actually not as major an undertaking as you at first might perceive, whether it’s a major leak or a minor one.

One of the easiest ways to find the failure point is using a water-based dye or food coloring, and a sheet of paper.

Wipe the outside of the tank completely and, with a little bit of help from another pair of hands, slide a sheet of paper under the tank.  Once the correct leaking corner is identified, you then need to confirm the exact spot. This is where the dye comes in as more often than not water tends to run along its merry way before exiting from the offending pinhole.

Using a syringe filled with colored water or food dye, either is fine as they are both harmless to fish, insert it close to the offending side and squirt out a small amount. Watch closely, and patiently, and soon you will see the water seep out of the exact spot where the pinhole is or where the silicone has peeled away imperceptibly from the glass.

Why not just strip out the complete silicone strip where the leak seems to be coming from, you may ask?

For two reasons.

First, the leak may be able to be repaired just from the outside of the tank, saving you a lot of time.

And second, it’s possible that the leak is solely at the top of the seam. In this case, just a small portion of the water would need to be drained out to just below this level, avoiding the hassle of having to completely drain all of the water out of the aquarium along with the fish.

If this is possible then it would be a case of allowing the affected area to dry, strip the sealant to the leakage point, and resealing that area with a new line of silicone.

The temptation to do a rush job can be irresistible, to just use a dollop of silicone on the outside to seal the hole or even to use some scotch tape as a quick plug. Both will seemingly work immediately.

But either quick fix may come back to haunt you, either not being sufficiently watertight enough to prevent a slow seepage in the not-too-distant future at the most unexpected moment.

So maybe this quick fix will work for a day, maybe for a week, or maybe even a month.

The weakness of this quick fix, basically, is that the water pressure from the inside of the tank will push from the inside out, pushing whatever patch you’ve put in place away from the tank, increasing the chances of a further leak.

If, however, the patch is on the inside and done well the pressure from the inside of the tank will push the patch further into the new seal, tightening it and decreasing the chances of a leak in the weeks or months to come.

The method of changing out the seal between two panes, whether a partial strip or a full peel away, is by using a cutting tool.

The old sealant needs to be sliced and peeled away from the glass above the point of leakage. Care needs to be taken to not cut away the silicone that sits between the two panels of glass, just the exterior silicone.

Then a scraper needs to be used to clean the area further, with care to be taken that no offcuts or small bits tumble in the water to be forgotten; fish are forever curious and will probably nibble on anything floating in the water and, even though the silicone is non-toxic, it is not beneficial for their digestive system.

Once the area is scraped clean then acetone should be used to wipe off any residue and foreign material; if the area is not properly prepared the new sealant may not adhere to the surface completely.

Finish the preparation by drying it off with a clean cloth or paper towel and letting it dry for a further 15 to 20 minutes.

The new silicone, non-toxic and suitable for aquariums, needs to be applied in a continuous line between the seam of the two panels. Then using your wet finger or a caulking tool, just smooth down the line so it bonds completely on both sides, filling any gaps.

For additional peace of mind, a silicone seal can be applied to the outside of the seam as well. And it can’t hurt to check the other seals that are exposed at the same time to make sure that they are all still in good condition.

Unfortunately, the new silicone doesn’t always bond well with the old and if that’s the case then the whole seam needs to be stripped out, the area cleaned and resealed. If the bond appears to be a good one, however, then the silicone patch needs to be left to dry properly for 24 to 48 hours at least.

After this curing period has passed, water can be poured into the tank up to a set level and a paper towel can be taped to the outside to check for any potential leaks. Monitor over the next couple of hours then fill to another level and repeat the process until the desired fill level is reached.

The last thing to verify, before re-admitting any fish that had had to be taken out, is to confirm that none of the new sealants have been loosened by the water pressure or improperly applied.

A Cracked Fish Tank

If there is an actual crack in one of the panes of the aquarium, that’s another kettle of fish, so to speak.

Again, similar to a leaking seal the level of water can be drained out below the leak point if it isn’t too low. If it is towards the bottom of the tank then it will probably be a matter of a full drain and rehousing the fish into a temporary domicile while the fix is undertaken.

Nine times out of ten this is normally the case and all the water will have to be emptied out of the aquarium. The advantage of a full drain is having more elbow room to enact repairs without having two dozen pairs of fish eyes scrutinizing your every move and the quality of your work. Intimidating.

So, in this case all the fish would have to go to temporary housing along with all the gravel, rocks, plants, everything, until the job is completed.

With the aquarium now emptied, the exposed area around the crack needs to be cleaned and dried off thoroughly, similarly as with a seam failure between two panels.

At this point, the next course of action depends on the severity of the crack itself.

Can it be repaired or does the whole panel need to be replaced?

A repair of a slight crack first involves ensuring that all moisture within the crack itself is eliminated. One of the best ways to do this is with a hairdryer so the area will be fully prepped for the next step.

Once the crack is completely dried the silicone can be smeared along the length of the cracks, and slightly beyond its edges for added security and full coverage. The finished result may not be pretty but if it does the job…

An alternative method, and possibly superior way, to repair the damaged area is the sandwich method.

Either buy or cut yourself two pieces of glass so they are long enough to overlap all the minute edges of the crack completely. Make sure to clean the surfaces of the new glass with acetone so the silicone will adhere to both surfaces and create a watertight seal. Then, similar to the above leaking solution, run some silicone along the cracked lines and then along the edges of the glass that is going to be the patch.

Press the cut glass gently into place and run a finishing line of silicone around the edges to complete the seal. Repeat this process on the other side.

At first glance this patch isn’t pretty, but it will solve the problem.

If you would prefer to have the full panel replaced it would be better to have a professional do an inspection and quote for the job. After receiving a price, the decision would be yours either to have the complete panel replaced or opt for buying a new aquarium.

If the patching method is the preferred option, a curing time would be recommended of about 48 hours or more and then the refilling process can begin, filling to set fill levels at a time over a few hours, waiting then adding more water until the final fill level is reached.

On an aquarium, all patches and fixes of this sort unfortunately create somewhat of a focal weak point due to the build-up of water pressure from within the tank, specifically in comparison to the other panels. Due care needs to be taken with the speed of the refill and to pay close attention to monitoring for any leaks over the following days.

If, after the obligatory waiting period, all is sealed watertight then the restoration process can begin.

Take the time to clean any plants before readmitting them and take advantage to perform any maintenance checks at this stage and then, once everything is back in its place, the fish can be transferred back into their home, safe and sound.

The Repaired Aquarium

For an aquarist an emotional attachment to an aquarium that has been in their possession for years can be hard to break. If a leak occurs an instant replacement is not foremost in the mind, a speedy repair is, and the first time a leak occurs it can be unnerving and unsettling.

Discovering a slow leak in an aquarium is not the end of the world if caught early. But a slow leak in an aquarium if caught late can be a disaster.

Armed with this new treasure trove of invaluable tips and tricks it should now be comforting to know that if there is ever a problem in the future, which can still occur in other potential weak points in the aquarium, that you now have the experience and knowledge to solve any leaking issues.

With this current crisis averted your aquarium, with its fragile ecosystem stabilized, can be enjoyed to its fullest extent once again.

Author Profile

Adam Edwards
Hi, my name is Adam and I'm an aquarium enthusiast! I didn't discover the joys of being an 'aquarium fanatic' (as some of my friends call me!) until I was in my 20's. When I first started out I found it difficult to find all the information I needed so I started this website to compile all the useful information I can think of. Enjoy!