Last Updated on April 24, 2023 by Coral Realm

It is easy to make simple mistakes whilst keeping a fish tank. You’ll have your aquarium’s best interests at heart, but a mistake can cost your fish their health, or worse. 

Hopefully this aquarium advice article can keep you from making these common mistakes!


Things Not To Do – Aquarium Advice

Aquarium Advice - Things Not To Do

Do Not Put Fish Into A Brand New Tank

A very important thing you need to do when setting up a brand new tank is to cycle it properly. 

This means that after you have set up the inside of the tank and added the water, and installed the filter, lights, heater, and anything else you have bought for your aquariums, you must leave the aquarium running without fish for a couple of weeks. 

This will allow beneficial bacteria to proliferate in the substrate and the filter media, meaning you will get the benefit of biological filtration.

Regularly test for nitrates and ammonia during the cycling period, as these chemicals are prone to fluctuate in a new tank. Once the levels have settled down then you know the cycling is complete.

If you add fish too early to a brand new tank they would be living in an environment with fluctuating water chemistry, which isn’t good for them at all.

Refrain From Using Cleaning Chemicals

Using cleaning chemicals is a big no. Your aquarium is a delicate ecosystem, and you do not want to do anything to upset it.

You might think that properly cleaning and disinfecting everything when you clean your tank is beneficial, but in fact it is the opposite. You risk putting dangerous toxins into the water.

No matter how much you scrub the disinfectant off, traces amounts may still enter your tank. 

We spoke before of how you want to cycle your tank to enable beneficial bacteria to grow in your tank, and putting chemicals on the filter media will kill this bacteria. So you’ll actually be doing more harm than good.

The best way to clean things from your aquarium is to rinse them thoroughly in water from your aquarium. Using tank water to clean whatever aquarium filter you have installed and any decorations in the tank will keep all bacteria present and you won’t introduce dangerous chemicals into the tank. 

You can also use a water conditioner to treat tap water before putting it in your tank. This will remove the harmful chemicals and make it safe for your fish. There are many different water conditioners, and even more for betta fish specifically!

Refrain From Overcleaning

You definitely do need to clean your aquarium regularly. Aquarium vacuum cleaners are definitely recommended, as they make it easy to clean the debris from the substrate. And thoroughly. But as said previously, your tank is a very delicate ecosystem, and you want to leave it be as much as possible.

This means that you don’t want to be cleaning every decoration at every cleaning. Clean only a couple of things at once, and the next cleaning clean something else.

This will keep your tank clean, but won’t disrupt the balance you’ve had to strive hard to create.

Never Replace More Than 20% Of The Water At A Time

This is for a similar reason as why you shouldn’t overclean your tank. Your aquarium is a delicate ecosystem in fine balance, and disrupting it too much will cause some troubles.

You want to keep as much of the beneficial bacteria in your tank as possible.

Replacing less than 20% of the water at a time will also help to regulate the temperature. It is very hard to get the replacement water exactly the same temperature as the water you already have in your tank. 

If you put in water which is a hugely different temperature you can cause your fish to go into shock. Using an aquarium thermometer is a good idea to keep this from happening, but replacing less than 20% of the water should mean that the temperature change is kept to a minimum.

You shouldn’t have to treat your water for chloramine or chlorine if you take 20% of the water or less either, as it is a little amount that should then be taken up by the filter.

Don’t Depend on Bottom-Dwelling Fish To Clean Substrate

AquariumadviceIt can be an easy mistake to make. If you have bottom-dwelling fish, or scavengers, such as Plecos which are constantly rooting through the substrate or cleaning the glass you might think that it doesn’t need cleaning.

You’ll be right in thinking it will help to keep the tank clean and tidy, but the substrate and glass definitely still needs a scrub. 

The scavengers will help to clear algae and leftover food, but detritus will still build up, so to keep your aquarium clean you’ll still need to clean the glass and substrate. 

An aquarium vacuum cleaner is invaluable if you don’t have one already.

Don’t Overcrowd Your Tank

Having too many fish in an aquarium can cause serious problems. Not only will your fish get in each other’s way and become more aggressive towards each other, it will also impact the water chemistry.

Your fish need the proper amount of space. Many species need to be able to retreat to a safe space when they feel threatened, or to have their own territory in the tank. 

If you overcrowd the aquarium, they won’t be able to have this and will get stressed. This stress will be exhibited not only in behavioral changes, but will cause health issues as well.

The water chemistry will be impacted by having too many fish as ammonia and nitrates will build up very rapidly, impacting their health.

Don’t Bulk Buy Fish

You shouldn’t really be buying more than 4 fish at a time. This is to maintain your tank’s current water chemistry. 

Fish do produce a lot of waste for small animals, and this waste causes a buildup of ammonia and other chemicals. The filter gets these out, but if you put too many fish in the aquarium at a time the waste produced might overwhelm it.

More fish also means more oxygen will be taken from the water, as they need oxygen just like us. If you add fish and they all act lethargic then you can add a wave maker, powerhead, or airstones to aerate the water.

You are much better served by adding 3 fish at a time, and letting your aquarium regulate itself before giving it another shock with more fish.

Don’t Overfeed Your Fish

Aquarium Advice OverfeedingOverfeeding fish has direct and indirect consequences on their health.

First of all overfeeding will cause your fish to become overweight and unhealthy. Some fish species are very sensitive to overfeeding and will balloon in weight when feed too much. 

Indirectly, giving your fish more fish food than they need will mean more waste. Food which sits uneaten at the bottom of the tank will slowly fester and can cause a build up of harmful chemicals and bacteria. If you don’t clean the tank regularly and clean to excess debris, it will mean that your water will look dirty and cloudy, and you will have to do more regular water changes. It can impact the health of your fish too.


Hopefully these points make sense and you have read some good aquarium advice in this article. These are the most commonly made mistakes that aquarists make, and they are incredibly easy to do. 

We’ve all been guilty of feeding our fish a bit too much after all!!

But if you follow these simple things to avoid, then your tank should flourish.

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Coral Realm

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