By Shahu Sardar*       

Regularly changing water in the aquarium is an important factor for maintaining a healthy environment in it. But for many beginners water change has proved to be a mishap. Many complain about death of fishes after a water change, which would mean that water changes are bad for the tank. But this is just the result of some common mistakes made by the hobbyist. 


Fishes are not alone in the tank; with them are plants and some good bacteria, all three interacting with each other to create an ecosystem. The fish waste produced contains toxic ammonia that is broken down into simpler, less toxic components by bacteria and is further taken up by plants.

The formation of this ecosystem and other changes are very slow. Any changes in water chemistry occurring naturally take place very slowly and thus fish get acclimatized to it.


It’s an irony that super clean water can kill your fish, than water that has bacteria and parasites in it. Large water changes that include more than 60% water change, rinsing gravel, cleaning filter media lead to a complete, massive change in the water chemistry. Fishes when put in these new conditions, lead to temperature shock, stress, loss of appetite, and then death.

 As stated earlier, tank water contains useful bacteria that help in keeping water free from toxic ammonia present in the fish waste. Large water changes lead to the elimination of these bacteria. Those living under the gravel get washed off while rinsing it and colonies get destroyed when we clean the filter sponges/filter media.  Fishes when produce fish waste containing ammonia remains in its toxic form due to the absence of these bacteria. The accumulation of ammonia leads to ammonia burns and then the death of the fish.


         Now reading the above context, it may seem that water changes are risky and not useful at all. But if we follow regular water changing, and some simple steps we could bring down the risk of killing the fish and disturbing the tank ecosystem.

Without water changes, the dissolved toxic waste would get accumulated, which will not harm the fish right away but will slowly damage its immune system, making the fish prone to dying even by small diseases or stress.

Having good bacteria in the tank also means presence of some amount of bad bacteria, parasites, and viruses. Fishes living in healthy water conditions will not get sick even when exposed to any disease. Also, as the water quality drops the number of parasites increases too.

When we talk about keeping a fish healthy and increasing its life span, the best thing you can do is keeping good water quality.


As stated earlier, some common mistakes lead to disturbance in normal conditions of the tank. Here we would know the right way of changing your fish tank’s water.

 Frequency of Water Change

Water changes should be scheduled for regular maintenance of the tank. It can be done on weekends or according to your convenience. Remember to keep them regular rather than occasional. A moderately stocked tank should undergo a 20% water change every week. A 50–60% water change should be conducted every 5–6 weeks to prevent any type of nitrate accumulations. If a fish dies or there is an outbreak of some disease, go for a 10% water change.

The Process

Here is a step-by-step process of a basic water change:

  • Unplug your heater, filter, and other equipment.
  • Vacuum out the water through a siphon and make sure all big-sized derbies come into it.
  • Clean the glass with an algae scraper or simply by an old brush.
  • Remove dead leaves, stems, or any other big-sized derbies by hand.
  • Any decoration if covered in algae can be scrubbed with a toothbrush. Make sure you just wash it with warm water without using soap.
  • Trim out dead stems or overgrown plants if any.
  • In a bucket of water add 2–3 drops of dechlorinator or any other water-treating liquid available in pet stores.
  • Slowly add new water. Make sure you don’t directly put it over the fish in the tank.
  • Switch on the filter and heater and keep the aquarium light switched off for 1–2 hours.

Tips for Water Change

–           Keep water changes scheduled. Know the time period for which the tank remains clean and plan water changes accordingly.

–           Never randomly do large water changes.

–           Don’t clean gravel and filter on the same day.

–           Clean the filter 2 days after the water change.

–           Clean the filter every 4–6 weeks rather than cleaning it weekly.

–           Always add dechlorinator in new water or let the water sit for a day before adding it to the tank.

–           Keep fishes in the tank during the regular 20–50% water changes. They can be moved in another tank during large water changes. 

These simple tricks would help you prevent the risk of dead fishes and disturbance in ecosystem of the tank.  

*Author is an Aquarium hobbyist and fishkeeping enthusiast from Pune. He has been in this hobby from the age of 10 and had really great time with fisheeping. He also runs his own fisheeping blog and aquarium service called the Aquanation, which provides free asistance to begginers in pursuing this hobby. He can be reached at 7774851593/

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