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9 Common Fishkeeping Mistakes and How to Avoid Them

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I am a pet lover who enjoys educating people about maintaining the fish in their aquariums.

A beautiful aquarium can be the center of your home, but watch out for making these common fishkeeping mistakes.

A beautiful aquarium can be the center of your home, but watch out for making these common fishkeeping mistakes.

Nine Common Errors in Fishkeeping

People who have an aquarium as a hobby usually make mistakes that lead to their fish becoming ill or even dying. Unsuccessful outcomes can cause a lot of frustration, and many will leave the hobby even though they have already invested heavily in equipment, medicine, and fish.

This is a list of common mistakes you might make, along with recommendations to avoid them.

  1. Overfeeding your fish
  2. Overcrowding your aquarium
  3. Becoming obsessed with your fish
  4. Not setting up adequate filtration
  5. Excessively cleaning your tank
  6. Using the wrong substrate
  7. Not adding plants to the tank
  8. Using excessive medication
  9. Taking advice from anybody
Avoid the temptation to feed your fish too much.

Avoid the temptation to feed your fish too much.

1. Overfeeding Your Fish

Do not overfeed your fish. If we stuff them, not only will there will be leftover food floating in the tank, but they will defecate excessively, which causes dirty water. Plus, when the organic matter decomposes, it will poison the water.


To avoid this, carefully follow the feeding instructions for each type of fish. Remember that fish are cold-blooded creatures. The lower the water temperature, the less active our friends will be, and, therefore, the less food you will need to give them. Even with active fish in warm water, you should only feed them in moderation (not more than what they can eat in two minutes without leaving any pieces on the bottom of the tank).

A good rule of thumb is to feed them once or twice a day. Never make the mistake of feeding them every time they ask for it.

There are too many fish in this tank.

There are too many fish in this tank.

2. Overcrowding Your Aquarium

Fish are living creatures that generate waste. This waste tends to spoil the delicate water. The more fish you keep, the more food is given, and the more waste is created. This results in an aquarium environment that is toxic and unstable.


Try to equip your aquarium with the correct ratio of fish per liter of water. This ratio can vary depending on the size of the fish, the water quality, and the filtration system you are using. You can apply the rule of 40 liters of water per adult fish, although this rule is flexible. If you have excellent filtration, the correct ratio will be lower, but in the case of a corrupt filtration system, the ratio will be much higher.

It is also important that you choose compatible species. You cannot mix aggressive fish, or they will fight each other. Likewise, fish with different water needs cannot be kept in the same aquarium.

3. Becoming Obsessed With Your Fish

Fish do not require constant care and attention. They are not like dogs who need frequent exercise and a lot of affection. You should stop trying to look for signs of illness all the time and stop placing or rearranging decorations, plants, and gravel. If you get obsessed, you’ll end up playing inside the aquarium every day, changing the water circulation, cleaning the filters and sand, and thus causing stress and problems for your fish.


If you want your fish to be happy and healthy, then leave things alone. Your aquarium does not have to be perfect, just in good living condition. A biologically active aquarium is achieved only when the water flow is stable, gravel is set, and filters are not handled. The best results are obtained with less care. An established aquarium becomes very stable and consumes nitrogen elements by itself.

Make sure you purchase a high-quality yet gentle filtration system.

Make sure you purchase a high-quality yet gentle filtration system.

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4. Not Setting Up Adequate Filtration

Aquariums usually come with simple, standard filters that you will need to upgrade if you want to give your fish the best living conditions.


Provide a superior filtration system recommended by filter manufacturers—but, at the same time, avoid ones that create strong water currents. You may also want to consider purchasing two filters.

Take, for example, an aquarium of 100 liters with a recommended 100-liter aquarium filter. In theory, this should be adequate. But if one day you have an excess amount of waste, the filter will not be able to handle it, and you’ll end up with a mess. So, to be sure that your aquarium water will be adequately filtered, I recommend getting an extra one of equal or greater capacity. Why? If one filter starts to fail or some debris gets stuck in it and reduces the water flow, there will always be another one to work as a backup.

It is also advisable to always have two filters because having opposite water currents will not create dead zones where debris can accumulate. By alternating between filters, you can ensure that the existing biological load in the aquarium is always able to decompose organic residues. Filters are the most expensive part of an aquarium, but they are necessary for keeping your beloved exotic fish happy.

Here's a secret: A healthy aquarium is always partially dirty! It's dangerous to keep your tank utterly spotless.

Here's a secret: A healthy aquarium is always partially dirty! It's dangerous to keep your tank utterly spotless.

5. Excessively Cleaning Your Tank

An aquarium should look clean, but the secret to a healthy aquarium is that it is always partially dirty. If you have a totally clean aquarium, you’ll only end up with "dead water,” which turns it into a breeding ground for diseases and problems. Dead water means that the water does not contain any beneficial bacteria that can help decompose waste.


Water changes need to be made only when the tests indicate so. You should track your water quality regularly to know when to do water changes, and you should not do them when you do not need to.

Cleaning your filters should not be associated with water changes. If you clean the filters when you change the water, you’ll be killing all the great bacteria that help reduce most of the spoilage from organic remains.

Not all gravels are created equal. Make sure you choose the right cover for the bottom of your tank.

Not all gravels are created equal. Make sure you choose the right cover for the bottom of your tank.

6. Using the Wrong Substrate

There are many kinds of gravel, but some are not ideal for fish aquariums.

  • Colored pebbles usually have dyes that can negatively affect the health of your fish.
  • Coarse gravel tends to accumulate feces and uneaten food that will rot and contaminate the water.
  • Excessively fine gravel tends to cause stagnant water that gets trapped below the surface of the gravel, which leads to rot and pollution.


Use the correct gravel: medium grain with no artificial colors. You could also add some volcanic gravel.

Plants help remove nitrate from your tank.

Plants help remove nitrate from your tank.

7. Not Adding Plants to the Tank

Having no plants means there will be no nitrate removal, and excess nitrate will poison your fish.


I recommend providing ample amounts of plants in each aquarium. Plants will eliminate nitrates through absorption and also tend to be very tasty and nutritional for your fish.

8. Using Excessive Medication

Fish do not need immediate treatment every time they are sick.


Treatments should be administered within reason, and you should be very knowledgeable about when medicine should be given and the required dosage. Remember that medicine is a poison designed to kill any organisms that attack your fish. If you give your fish the incorrect dosage, it will kill them instead. Before administering medicine, follow the advice of experts and ask what the recommended dose is.

Finally, remember that not all illnesses can be cured by using treatments. It is better to move the fish to a separate tank with clean water, tranquility, and peace so that they can recover in a more natural way.

9. Taking Advice From Anybody

Many people are not qualified to give advice about keeping aquariums, especially fish sellers. They might not be acting in bad faith, but they have a business to sustain. They have to make sales, so many of them will not hesitate when giving you bad advice, as long as it allows them to close a good deal.

Among people who are not prepared to advise others are those who visit online forums. It is not uncommon to see cases where poorly informed suggestions about medications and dosages are passed around. Many fish have died because people take bad advice from forums.


When buying fish or aquarium equipment, it is important to consider a second opinion. If you ask something in a forum, do not run away with the first answer. Wait for second opinions if things do not seem clear.

Be Patient and Focus on Your Aquarium's Health

Be patient. Like everything in life, having an aquarium takes time. You wouldn’t try to fix the world in an hour, so you shouldn’t expect your aquarium to be in tip-top shape in one morning. Patience, good advice, good accessories, and a desire to have a healthy aquarium are the right ingredients for a successful hobby.

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