Conducting frequent and routine water change is the most effective way to prevent and treat a plethora of problems that any aquarist may encounter.


Imagine performing all your daily activities in an enclosed room for the rest of your life. We all need change including fish. An aquarium is an enclosed environment; that is, the fishes swim, breathe, eat and excrete in the same water everyday and it’s not very pleasant after a while as fish waste, uneaten food and debris will build up in the aquarium increasing the level of ammonia and nitrate which will have harmful effects on your aquarium.

And the solution to pollution is dilution. 

A Fundamental Aspect

Water change is the fundamental aspect of aquarium maintenance. It will help remove all the pollutants and toxins in the water including decaying plant material, fish waste, leftover food, dirt and debris, ammonia, nitrates, nitrites and phosphates. Nitrates can further promote the growth of algae.

Trace elements and minerals in the aquarium are also beneficial for your fish’s health and development and these tend to get consumed over time and hence they need to be re-added. A failure or negligence in doing so will lower the pH of the water and affect the health of your fish.

Filtration Alone Cannot Counterbalance

With the advent of filtration systems and many chemical filter media, the importance of water changes is being overlooked. Filtration systems alone cannot counterbalance the harmful pollutants in the water.

The advantages of water changes are long term, they will help keep your aquarium healthy for your fishes to thrive. The aphorism- “Prevention is better than cure” is apposite here. You should do routine water changes without fail as negligence for the same will change your tank’s water parameters, eventually killing all your fish.


In short, the benefits of water changes are that they –

  1. reduce and control nitrogenous pollutants such as ammonia, nitrates, nitrites, as well as algae.
  2. remove organic waste (fish waste, leftover food, debris, decaying plant matter etc.).
  3. maintain the water chemistry by restoring the used up or filtered out trace elements and minerals which are indispensable for your fish’s health and vigor.
  4. improve the water clarity by removing cloudiness and discoloration.


As a rule of thumb, you should change the water atleast 10-20% every week depending on the tank capacity and no. of fishes it has. However, smaller, regular water changes of 15-30% every week is recommended for densely stocked aquarium or aquarium with large fish.

For goldfish tank of atleast 100 litres capacity, we recommend doing a water change of atleast 30-40% every week, and cleaning filter every alternate week.

The frequency of water change depends on many factors and a long gap between two water change will enable the water chemistry to change too much which is not good. Do consider the following points while performing a water change –

  1. Some species or communities will require a more frequent water change than others.
  2. A highly stocked aquarium will need frequent water changes as compared to a lightly stocked tank as the production of waste and toxins will be more.
  3. To reduce stress in fish, it is recommended to change a smaller percentage of water more frequently than changing a larger percentage once in a while.
  4. Do regular water tests – you should change your water immediately when there’s an increase in the level of nitrate. Regular water changes will also prevent or reduce other potentially hazardous toxins and pollutants.
  5. You should use a gravel siphon to vacuum the substrate while doing a water change as it will help remove any debris, dirt, uneaten food and other waste from the gravel.
  6. You should also do frequent water changes if your fish are being medicated for any illness. This will boost up the healing process. Keep the water as clean as possible.

Most importantly, remember not to change too much of water or all the water at once as it will tear down your aquarium’s ecosystem. Water parameters will fluctuate and it will destroy the beneficial bacteria in the aquarium. A large change will cause a large fluctuation and cause shock to fishes, even leading to death.

Final Tips

  • Clean the substrate – vacuum the substrate while you’re siphoning the water
  • Don’t touch the filter – cleaning the filter and performing a water change at the same time can wipe out the essential beneficial bacteria. 
  • Remember that adding water is not the same as changing the water. Simply adding water will change the water chemistry but will not remove any waste.
  • Degas the water by letting it sit still for a day which will dissipate dissolved gases that might be detrimental to the fish.
  • Prepare a schedule for aquarium maintenance to avoid forgetting.
  • If you’re using tap water, do not forget to use a dechlorinator to remove chlorine and chloramines.
  • If you’re use R.O. water, either mix it with at least a third tap water to introduce some hardness, or better still use a mineral/buffering additive.
  • Make sure the water temperature and water chemistry matches while you’re carrying out a water change; especially if you’re doing larger water changes.

Additional Reading – Aquarium Maintainence

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