Freshwater Fish

Basic care of Carassius Auratus fish

You’ve purchased an aquarium kit, which probably includes an aquarium, gravel, an internal filter, water conditioner, flake fish food, and a net.

Assembling the aquarium for your Carassius Auratus

Place the aquarium in a place that does not receive a lot of direct sunlight. Bright areas can lead to excessive algae growth as well as temperature fluctuations, which are also detrimental to fish.

Wash the gravel well in a bucket of cold tap water until the water runs clear. If you have a lot of gravel (for example, if you bought a larger tank), wash the gravel in small amounts, as it actually cleans faster that way.

Carefully place a layer of gravel on the bottom of the aquarium and then proceed to fill the tank with tap water until it is almost full. Place the internal filter in the water, attaching it to the back or side glass with the suction cups provided.

Prepare the aquarium water

At this stage, you add the required amount of water conditioner, which removes chlorine from tap water. Chlorine makes the water safe to drink, but it is very harmful to aquatic life.

Turn on the filter and for the next few days the vital process of cycling the aquarium will begin. During this time, check that all equipment is working as it should.

The filter must be left running 24 hours a day, 7 days a week. This is because a colony of friendly bacteria will gradually build up on the filter sponges, and it is these bacteria that break down fish waste into less harmful end products and keep fish safe from poisoning.

That is why it is very important that the filter remains on at all times or these vital bacteria will die.

Adding a quality bacterial starter supplement to the aquarium water will help get the biological filter up and running in less time.

The filter maturation period actually takes several weeks, and during this time it is a good idea to test the water via a water test to ensure that the aquarium filter is working properly.

Enter your first Carassius Auratus

After a few weeks, it will be time to buy your first Carassius Auratus. It is essential that the tank is filled with fish very slowly, adding one or two fish at a time. Once you bring the fish/fishes home, float the bag for about half an hour to even out the temperature before gently releasing the fish.

As tempting as it may be to turn on the aquarium light, leave your fish in the dark for a few hours while they settle into their new environment.

20-25% of the tank water should be changed a couple of times a week to dilute the nitrates left behind when the Carassius auratus’ waste is processed by the bacteria in the filter. You can consult our guide When And How To Change The Aquarium Water?

Nitrate, while not as deadly as the fish waste itself, can be harmful at high levels and also causes unsightly algae. So make sure you do regular partial water changes to dilute the nitrate and replenish the tank with some fresh water.

Never change all the water at once, as this will kill the bacteria in the filter. When you add new water to the tank, first make sure it has been treated with a dechlorinator.


When the tank is newly set up and you have added your first Carassius Auratus fish, feed it a very small amount, once every two days.

Overfeeding, particularly in the early stages when the filter is still maturing, can cause serious problems as there will be too much debris for the filter bacteria to deal with. The fish will be absolutely fine if they are fed every other day, and offering them too much food will actually do more harm than good.

aquarium maintenance

After a few weeks, with the filter fully mature. You can increase feeding to once a day and reduce water changes to 20-25% once a week.

Water changes should be carried out regularly because, as mentioned above, the bacteria in the filter only change harmful chemical wastes into less harmful ones, and these still need to be diluted.

Cleaning and changing the filter

Also, now is the time to start cleaning the filter sponge, a process that only needs to be done once every 6 weeks.

Turn off the filter, remove the sponge and squeeze it into a bucket of mature aquarium water you’ve taken out of the tank (this can coincide with a water change). NEVER rinse the sponge under the tap, as the chlorine in the tap water will kill all vital bacteria.

Sponges don’t need to be spotless, and it doesn’t matter if they’re discolored. The only time they will need to be replaced is when they don’t spring back after tightening. And when you do this, replace only HALF of the sponges at a time, to preserve as many beneficial bacteria as possible; never replace all sponges at once.

Cut the sponge in half to do this if necessary, then the remaining half can be replaced after a few weeks. Put the filter back in operation as soon as possible after rinsing the sponges to minimize the loss of bacteria.

Tank and gravel cleaning

From time to time you may need to clean the front glass with an algae pad/magnet to improve viewing. The gravel will also need to be cleaned periodically with a gravel vacuum, as this will remove any debris particles missed by the filter.

If all of this sounds daunting to you, don’t worry: once it gets going, there’s probably less than an hour of work a month, including water changes, gravel vacuuming, water testing, algae cleaning, feeding, and, occasionally, some maintenance filter.

If you want to delve deeper into this beautiful hobby, we recommend you take a look at our guide My first aquarium: Aquarium hobby for beginners, and also our Goldfish Care Guide.

Just keep in mind that given ideal water conditions and enough space, Carassius Auratus fish have been known to grow to over 30cm in length and live for over 25 years.

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