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Top 7 Mistakes New Aquarists Make

Starting in the world of fishkeeping can seem an easy hobby from the outside looking in. Tank? Check. Water? Check. Fish? Check. I had a simplistic view of it too before starting. However once I got into it I realised that to be a really successful aquarist in terms of keeping your fish alive and in good health there are a number of things you must learn.


I’ve compiled a list of mistakes to avoid when setting up your tank for the first time, some of these I learned from experience, others from doing research online or speaking to other aquarists.

If you have any tips of your own feel free to post them in the comments!


1. Not cycling a tank before adding fish

This is a major one, that could lead to disaster if not done correctly. Cycling a tank is the process of creating a safe and liveable environment for your fish before putting them in the tank. his matters because fish create waste which produces ammonia. Any amount of ammonia is toxic to fish, however bacteria will accumulate over time to break this ammonia down to less toxic substances.

So what many people do when buying fish for children as a present is buy the tank and fish only days apart. They do not promote bacteria production by adding a few flakes of fish food to the water everyday and instead just put the fish in after a day or two when the water settles. This leads to high levels of ammonia being present in the tank after a few days which lowers the fishes immune systems capabilities and they become susceptible to illness and many less hardy fish die during this stage.


On average it can take two weeks for a tank to cycle fully. This means that putting fish into an environment when all the bacteria required to maintain the tanks ecosystem are present and the fish will not suffer.


 2. Overstocking on fish

Adding too many fish to your tank can cause problems for filtration. In your local fish stores the tanks have sometimes up to 50 fish in one 60L tank. The stores have staff who clean the tanks and carry out water changes daily. They also have a centralised filtering system which can cope with the large numbers of fish and the heavy duty filtering that’s required.

Depending on your tank set up and quality of the filter you may find that you can stock more than the recommended guideline of 1ch of fish per gallon (4.54L)  of water. I have a Fluval U2 in a 60L tank and it is overkill for the size but the standard filter that came with the Korall 60 wasn’t up to spec with my 20 fish. Since upgrading the ammonia levels and clarity of the water has been perfect.

overstocked fish tank
Not a good idea!


Overstocking a cause consistently high ammonia levels, this cause lead to the death of your fish, which can obviously be expensive in the long term and cause needless suffering to your fish. So stay within your tanks limits or upgrade your filter to above requirements.


 3. Inconsistent Tank Maintenence

As with anything it takes a little while to get into a habit with new hobbies. New fishkeepers can sometimes slip into inconsistent routines for water changes. It’s important to consistently change the tank water for various reasons.

Firstly to keep levels of nitrates down. During the nitrogen cycle ammonia is converted to nitrites, then nitrites to nitrates. While nitrates are not toxic in low levels to fish, when they accumulate they are. The only way to get rid of them is to perform water changes weekly, 30% is the advised amount.

The second reason is to keep algae from taking over your tank. Algae thrive in places where water is stagnant such as ponds. The most natural way to stem algae growth is to change a little bit of water often.

A quick video on water changes.


4. Overfeeding

Something so simple yet often overlooked. Fish will always appear ravenous when being fed which can lead fishkeepers to feed them more. However this can be detrimental to you fish and your tanks ecosystem. Fish food that lands at the bottom of the tank will break down into ammonia and cause the same issues that overstocking can cause.

Fish generally do not need to eat everyday, in the wild they are opportunistic and eat when they are hungry and if food is available. This is why they will give the appearance of being starving when fed even though this may not necessarily be the case. They can go days without being fed, though this isn’t the best solution either. It’s normal to feed them a few days then allow a days gap between more. This keeps your ammonia levels down, also be sure to not give them too much. The general rule of thumb is that they should be able to consume the food within 5 minutes.


5. Not quarantining sick fish

I myself have been guilty of this when first starting out as I wasn’t aware of the signs of a sickly fish. Quarantine tanks can be very helpful in the prevention of disease outbreaks. There’s two main benefits to having a quarantine tank at hand, first is that you can separate sick fish and second you can protect the healthy fish from potentially harsh chemicals that are used to treat some diseases.

Quarantine tanks do not need to be large or expensive, small plastic tanks can be used. Do not use any substrate in this tank, but the fish will need sense of having a “bottom” so place the tank on a black bag or paint the bottom, this will lower their stress levels. The tank will need a heater and filter.

Simple Quarantine Tank
Simple Quarantine Tank


6. Mixing incompatible fish types

Tank mate compatibility is crucial to having a successful and healthy freshwater aquarium. Incompatible species will increase stress in the aquarium, which could result in disease and considerable loss. Use the chart below as a guideline before making your fish selection.

Remember, no guarantees can be made about the compatibility or incompatibility of any particular species of fish. Also, particular species within a group of fish vary in temperament and may not correspond with the guidelines below.

Compatibility Chart
Compatibility Chart


7. Introducing new fish properly

Correctly introducing new fish to your aquarium is important not only for the health of the new fish, but for your existing fish as well. When incompatible fish are added to an aquarium, the weakest fish will be stressed, which could result in disease that affects all of the inhabitants of the tank.

See the procedures outlined on the acclimation for new fish page for detailed instructions.

Here are a few tips we recommend to make the transition to its new home as stress-free as possible for your new tankmate:

  • Make sure you have adequate hiding places for your new arrivals. Rocks, plants, and other sheltering areas will reduce aggression and thus stress in the aquarium.
  • It should go without saying that maintaining good water conditions through proper maintenance to ensure a healthy environment during this stressful period.
  • Try to add more than one fish at a time to an established aquarium. The chance of one particular individual being singled out and harassed will be minimized.
  • Always feed your aquarium before any new fish are introduced. This will help to reduce aggression toward new tankmates.
  • Rearrange decorations in the aquarium before the introduction to distract existing fish and remove established territories. This will help the new fish by putting it on equal ground as new territories are developed by all tankmates.

I hope these tips help! Happy hobbying.


About Mike

Web designer, football fan and budding traveller.

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