Fish Tank Maintenance

Fish Tank Maintenance

To keep your fish happy and healthy, you will need to perform a few regular maintenance jobs. This includes a partial water change and water testing.

Changing your Tank Water

Because your tank is an enclosed ecosystem, waste can build up and turn toxic. A smaller tank will have this occur at a faster rate than a larger tank, as will tanks with a large fish population.

To ensure your fish stay healthy, it is recommended to do a water change every two weeks (as a guide, this may be needed more or less depending on your tank).

  • Use a gravel vacuum and bucket. A gravel vacuum acts as a siphon and removes water from your aquarium whilst getting in and under the gravel and removing excess dirt and waste.
  • Whilst the water is siphoning through the gravel vacuum, move the end that is inside of the tank all through your gravel. Keep doing this until you have removed about 25% of the tank’s water capacity.

If you have a tropical tank, be careful not to drop the water level as low as the heater, as having your heater switched on and out of water will cause damage and compromise its efficiency.


Only ever change about 25-30% of the water in your tank. Removing any more will affect the biological filter. In other words: it would be like starting the set-up of your tank all over again. However, you may need to remove more if your fish have become ill.

  • Once you have taken out your water, replace this with fresh tap water. Ensure this is completed slowly, especially in a tropical tank to ensure the temperature does not change too much.
  • Treat the new tank water. Generally, you will use the same treatments you added when first setting up your tank, especially ammonia, chlorine and chloramine eliminator. Speak to your local PETstock team about which treatments you should keep on hand at all times.

Controlling Algae in your Fish Tank

Wiping the inside of your tank with a sponge or similar (free of any chemicals or soaps) will remove any algae or dirt build up.

To keep algae levels in your tank to a minimum:

  • Ensure your tank is out of direct sunlight
  • Only have your light on for no more than eight hours per day
  • Ensure your filter is up to the job

If you keep tropical fish, the addition of any catfish may also help to keep algae levels down as they like to consume this. If algae has become a problem in your tank, there are treatments available to help fix the problem.

Maintaining your Fish Tank Filter

Your filter has a number of parts that will need to be tended to. This includes:

  • Carbon – change every six to eight weeks
  • Filter cartridge – change every six to eight weeks (these normally contain carbon)
  • Sponges – maintain every two to three months. Ensure you’re rinsing in treated water as the chemicals in tap water will kill your good bacteria on contact.
  • Ceramic noodles – change every six months, ensuring enough bio-filter to sustain the tank’s system.
  • Impeller and rubber diaphragms – change when broken


The water parameters in your tank will change over time and become unsuitable for your fish’s survival. It is recommended to test these parameters on a weekly basis.

You will need to test pH, GH, Ammonia, nitrate and nitrite. You can do this yourself at home with a test kit or your local PETstock team will check them for you for free. Simply bring a tank water sample into store in a clean container with a lid.

If you find your test results to be undesirable, speak to your local PETstock Person about the best solution for you. Usually, the most common course of action is a water change or the use of pH adjusting powders.

Our Recommended Products

API GH/KH Hardness Test Kit

  • Tests tap water and freshwater aquariums for general water hardness (GH) and carbonate hardness (KH).

API Ammonia Test Kit - Fresh/Saltwater

  • Quick and convenient way to check the ammonia levels in your aquarium.
  • Catch and cure problems before they develop with regular testing.

Blue Planet Ph Kit Complete Freshwater

  • This kit allows you to know where your aquarium is now, and then by using the pH Up and Down powders included in this pack you can adjust to the desired pH level


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