9 Aquarium Maintenance Routine Mistakes Everyone Makes (and How to Avoid Them)

Charlie Morton

Charlie Morton


common aquarium maintenance mistakes

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There’s so much to learn about routine aquarium maintenance that it can take a while to learn the ropes, and longer still to become a maintenance master at all times!

In reality, most of us have made many routine maintenance errors, especially when we were starting out with our first fish tank. Occasionally, even experts still make mistakes that cost their fish’s lives.

While not everyone has made all of the following mistakes, most of us have made at least a few of them at some time or another. I sincerely hope this list will help you not have to learn the hard way!

Common Aquarium Maintenance Mistakes

We’ll start our list with the real rookie errors that first-time fishkeepers often make, before moving on to blunders that can trip up even advanced aquarists!

Incorrect Lighting Schedule

This is coming in at number one for good reason! In fish care guides, the lighting schedule is rarely mentioned. So rarely, that beginners could be mistaken for thinking that it’s not important.

In reality, almost all fish need day and night, just as most terrestrial animals do. If you neglect this step and leave the lights on all night or forget to turn them on in the morning, your fish’s biological clock will fall out of sync, potentially causing severe stress and illness.

Between 8-12 hours of light time is the usual recommendation for most tanks, with 10 hours being a good default point. After this, the lights should be switched off to give the fish enough time to rest and recuperate.

The easiest way to set up the ideal lighting schedule is to install a timer switch so your lights turn on and off every day at the same time without you even needing to be at home.

Chlorine and Soap Poisoning

Two more fatal errors that beginners sometimes make is exposing their fish to chlorine or soap – both of which are extremely toxic to fish.

Because chlorine and chloramine are almost universally added to municipal tap water across the world, it’s essential to remove these additives before adding tap water to your tank. According to cafishvet.com, chlorine poisoning typically makes fish suffer from oxygen depletion, damage to gill tissue, trouble swimming, and sudden death.

Even more deadly to fish than chlorine are soaps and detergents. Sadly, online forums are full of accounts of fish keepers who have unwittingly scrubbed their fish tank with a brush that had some dish soap on it, only to find their fish dead in the morning.

According to lenntech.com, even traces of 15 parts per million of detergent in the water will kill most fish. Fish eggs are even more sensitive to soap, which explains why household cleaning products washed into natural water sources are such a disaster for the fish that live there.

Neglecting to Clean Gravel

Novice fish keepers often don’t realize that gravel cleaning is an essential part of routine aquarium maintenance. I’m personally surprised how infrequently gravel cleaning is mentioned in aquarium care guides, since without it, tank conditions get toxic pretty quickly.

When I got my first fish tank in my teens, I had never heard of a gravel vacuum. Luckily, when my uncle came to stay, he explained the importance of gravel cleaning when making partial water changes.

The first time I vacuumed my gravel, huge clouds of detritus got sucked up and dumped in the bucket. I quickly saw how, without doing this, the gravel would become saturated and severely mar the tank’s water quality.

You can make a simple homemade gravel vacuum with a plastic bottle cut in half and a hose pipe, or buy a purpose-made model. We’ve compiled a buyer’s guide for the best gravel hoovers on the market, with more details on how to use them, here.


There are very few fish keepers who can hold their hands up and say they’ve never overfed their fish. Overfeeding is probably the most common and most fatal mistake that fish keepers make, and it’s and it’s easy to see how it happens.

Fish require amazingly little food yet appear to be perpetually hungry. It can be tempting to give in to their constant begging for more, or simply assume that they must require more than the tiny pinch that is prescribed.

Watch closely, and you may discover that while your fish’s instinct is to eat at every opportunity, a full fish will often spit out a chewed-up cloud of fish food minutes after eating it, or worse, become bloated, constipated, or suffer from swim bladder problems.

Overfeeding either results in uneaten food or excessive fish waste polluting the tank water. Poor water quality, oxygen depletion, and dangerous levels of ammonia, nitrites, or nitrates follow, causing algae blooms, illness, and frequently the death of the tank’s fish.

Instead, try following the default rule of thumb: Feed your fish just twice a day, with no more than they can eat in two minutes. Make minor adjustments from there if necessary.

Killing Your Biological Filter

Aquarium Maintenance Routine Mistakes Everyone Makes

While every fish keeper should know that cleaning their filter sponge is essential routine maintenance, some people fail to realize how important it is how you do it.

A biological filter is so-called because of the millions of beneficial bacteria that live inside the media, performing the essential role of neutralizing ammonia and nitrites to prevent your fish from being poisoned. Biological filter media normally includes some type of sponge inside your filter housing.

If the beneficial bacteria are killed off in large enough numbers, the biological filter will fail to do its job, ammonia poisoning will result, and it may take substantial time to build up a healthy colony again.

When cleaning your biological filter, it’s essential to only use either water from your fish tank, or dechlorinated, treated tap water and only rinse it gently. Untreated tap water or cleaning products are lethal biological filters so avoid them at all costs!

Too Large Partial Water Changes

Aquarium care guides generally recommend 20-30% partial water changes every week for tanks with a high bioload, or up to every two weeks for tanks that are lightly stocked.

The reason that it’s not recommended to change more than 40% of your tank’s water at any one time is the same reason that we discussed for the biological filter: Changing such a large proportion of your water in one go risks knocking out too many of your aquarium’s beneficial bacteria, thus risking ammonia spikes.

In emergency scenarios, 45% water changes are permissible, but any larger than that and you’re seriously risking disrupting your tank’s finely balanced ecology.

Another reason is that if your tap water has significantly different water chemistry to your tank’s water, it could shock your fish. To be on the safe side it’s better to match the new water pH and hardness with your tank’s water reasonably closely in any case.

Another mistake regarding water changes is newbies who refill their tropical tanks with cold water. Because this can easily cause fatal thermal shock in your fish, always ensure matching water temperature before refilling your tank!

Forgetting Daily Observations

One fish care mistake that even advanced fish keepers can make from time to time is neglecting to give their fish enough daily observation time.

Daily checks are essential to monitor each fish’s health and behavior. You must ensure there’s a harmonious relationship between your fish and that nobody is becoming too aggressive or a victim of bullying. It’s also essential to check for signs of disease every day.

If certain individuals are beginning to look stressed, lethargic, or losing color, it’s a tell-tale sign that something’s amiss. Early diagnosis can often be the difference between a dead fish, and one that quickly recovers after appropriate intervention.

Not only are these checks an essential part of proper tank care, but having the discipline to observe your fish every day will make you stand apart from mediocre fish keepers, as well as help you forge a deeper bond and appreciation for your fish!

Neglecting Water Tests

Another maintenance aspect that trips up both beginners and experts is water tests. If everything appears to be looking okay in your tank, it can be tempting to forego the routine water test, deeming it unnecessary.

But water tests often reveal things happening in the tank that can’t be noticed any other way. For example, if water pH is gradually becoming too acidic, it’s wise to start working on correcting it before your fish show any ill symptoms.

Likewise, if water tests reveal nitrate levels are getting too high, you may need to perform more water changes and work to solve the cause of the problem before your tank suffers algae blooms and sick fish.

For medium to large aquariums, test your water at least once a month or anytime you notice something unusual. For smaller tanks of 20 gallons or under, I’d recommend testing your water every two weeks.

Failing To Test Equipment

Our last error that even the pros sometimes make is failing to test or monitor their aquarium equipment. Both heaters and filters are so essential to a healthy aquarium that malfunctioning even for one day could cost your fish’s lives.

The easiest way to monitor your aquarium heater is to install a reliable thermometer and check it every day without fail to ensure your water is within the right temperature range. If you notice even occasional inconsistencies, it might mean your heater is becoming unreliable and needs replacing.

As for checking that your filter is working, simply make sure that it’s producing a healthy flow every day. Position your filter so that it either creates a visible current at the water’s surface or so you can see its current swaying some plant leaves. That way you can see at a glance that your filter is doing the job that it should.

In case either filter or heater breaks, it’s a great idea to have some backup equipment for emergencies.

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