How Often Should You Change Your Fish Tank Water?

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Written By Fun Fish Tanks

I Love my Fishes 

If you want to keep your fish and other live plants happy and healthy, regular maintenance of the water tank and changing the water is unavoidable. But you can’t just change the fish tank water without any plan. If you find yourself questioning how often should you change your fish tank water, you’ve come to the right place.

Generally, at least a 10-15% water change once a week is necessary if your fish tank is optimally stocked. You don’t necessarily need to remove the fish during the process. Just use a gravel cleaner to stir the gravel when changing the water. 

But of course, every tank is different from the other and you must understand how much bioload your tank has. Depending on how stocked your tank is, you will need a more individualized routine to change the fish tank water. I will share all about it in greater detail in the rest of the article. 

Why Is It Important to Change Fish Tank Water?

Not changing fish tank water frequently can lead to numerous issues. This is because no matter how cute and fresh they might look in your aquarium, they are not meant to live in it. The tank water gets polluted quickly due to their wastes. Even in nature, fish are not adapted to live in their waste.

To break down their wastes, you must use biological filtration or frequently change the tank water. Neglecting either of these practices can lead your pet fishes to get poisoned and eventually die due to their bodily fluids.

If you don’t do water changes your water will appear clear but a little turbulence will bring out all the dirt that has built up. These are the waste products of your fish that accumulate on the base of your aquarium. There are also a lot of chemicals that the waste products of the fish generate that prove to be toxic to your fish.

These are ammonia, nitrite, and nitrates. Unlike the substrates, you will not be able to see these chemicals with your naked eye and you will be unaware of the amount of the chemicals that have built up unless you use an aquarium testing kit. These chemicals need to be controlled within your aquarium and water changes help a lot in keeping these under control.

The stability of the pH levels and other minerals will also remain balanced by doing water changes. Not changing the water will also lead to the growth of algae. The higher the algae are in your tank the dirtier your tank will appear and it is bad for your fish too.

So if you want these precious creatures to live in your aquarium without suffering from any serious problems, you need to change the water frequently.

Problems Solved by Changing Fish Tank Water – Benefits

Neglecting to change your fish tank water doesn’t only cause an odorous, unsightly and unpleasant aquarium. It can even cause your precious fishes and other living inhabitants to suffer from various other issues.

So let’s look at exactly why changing fish tank water regularly is so crucial and what problems it can solve –

1. Prevents Any Solid Waste or Detritus From Building Up

Of course like any other living creature, your fishes poop as well. So whatever food they take in will eventually come out as urine or feces. Furthermore, all the uneaten food sink to the bottom and slowly decays. All these contribute to terrible water quality.

If you don’t change the tank water regularly, these waste products will keep on building up inside the water. Eventually, the waste products accumulate as solid debris in the bottom of your tank.

By changing the water regularly, you are preventing such solid waste or detritus from building up which can lead to dangerous problems later on.

2. Reduces Harmful Chemical Concentration

If you are not regularly changing your fish tank water, dissolved chemicals like phosphate or nitrate can slowly build up to reach dangerous levels. A high level of such harmful chemical concentration can lead to your precious fishes suffering from dangerous problems.

When you start to regularly change the tank water, it will also help to bring down the phosphate levels and remove tannins and staining. Moreover, it helps to maintain an optimum level of pH and KH.

3. Helps to Replenish Minerals and Trace Elements

To stay happy and healthy, your cute little fishes need vitamins and minerals as well. That’s why it’s crucial to give them new water regularly. Over time, minerals and trace elements in the water get either filtered out or used up.

These important minerals and elements are vital for stabilizing the tank water’s chemistry and your fish. To help your cute pet fishes to grow up strongly, make sure they get their daily dose of trace elements by changing the water regularly after a specific time.

How Frequently and How Often Should You Change Fish Tank Water

Ideally, you should create a schedule to change the water of your fish tank at least once every two weeks.

However, it’s best to change a portion of the water every week. If you opt for changing it every two weeks, aim for a 25% change. If you have the time to change the fish tank water every week, you can change only 10% to 15% of the water.

But the truth is that not every tank is the same and how frequently you need to change the water will depend largely on your tank’s bio-load. No doubt, the more fish your aquarium has, the more bioload it will accumulate.

If your tank has a higher number of fishes you should increase it to 20-25 percent. You should do a water change every week. Also, don’t forget to use a dechlorinator otherwise all the nitrifying bacteria will die because of the chlorine present in the water.

So first, you need to figure out how much waste is getting produced inside your tank. A simple way to do this is by testing the nitrates level in your tank water.

Ideally, your target should be to always keep the nitrate level under 40 ppm. For example, if your tank produces 5 ppm nitrate each week, it will eventually reach the maximum level in 8 weeks. When the nitrate level reaches the maximum level, you can change 25% of the tank water to reduce the nitrate level by 25%.

After the water change, the nitrate level should be around 30 ppm and will return to 40 ppm within 2 weeks. By keeping up with this current trend, you can develop a schedule to change 25% of the water every 2 weeks and keep it below 40 ppm.

Tips for Changing Water of Fish Tank

Here are some useful tips to changing the water of your fish tank properly:

  • If your fish tank is too small, a gravel vacuum may remove too much water at once. So a cup can be more useful to scoop the water out of the tank. You’ll need to siphon the tank from time to time. You can do this using a small tube.
  • Consider investing in a battery-operated siphon to make changing water easier.
  • When siphoning, taking the water from the bottom of your tank helps to remove as much mulm as possible.
  • Before siphoning, you can rake through the gravel bed to release the mulm stuck in the sand.
  • Remove all the large pieces of debris before it clogs the siphon hose. 
  • A vacuum does wonders if you use it to clean the substrate. You can get a vacuum from aquarium stores nearby. But don’t clean the substrate and filter together, as nitrifying bacteria thrive on these locations so it is not wise to clean these two together.


Regularly maintaining your aquarium is extremely important. But it requires you to change the water in your tank regularly as well. In this article I have extensively discussed how often should you change your fish tank water.

So,I hope you do not have any more confusion about the topic after going through the entire article.

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