How Often Do You Have to Change Water in a Fish Tank?

Hobbyists often need to make water changes in order to imitate nature. Many waterways have very low levels of nitrates because wastewater is constantly being flushed downstream. Unfortunately, nitrates is the side effect of feeding fish. Fish will be healthier if this parameter is maintained at a low level.

Generally below 40 parts per million is considered safe for most fish. This can be easily controlled by changing the water. It is easy to change water. We want to take water out that has nitrates in it and replace it with water that does not. I want to be able to control the water quality. Many hobbyists just change their water once a month. You’ll often hear hobbyists say, “change your water every other month.” But there are also those who insist on changing it every week. You can also find discus breeders that do it every day! Who is right?

They can be both right and wrong simultaneously. They are correct that they have a schedule that works for them. They are all wrong to recommend a particular water change schedule. Better is to help the person evaluate their water changing needs. First we need to realize that every tank will have a different water change schedule. Each tank will have a unique bio-load. The bio-load is determined by the amount of fish and food consumed. It’s not hard to understand that more fish will be thrown away if there is more food. A decrease in fish and food would mean less waste. We need to figure out how much waste we’re producing. This can be accomplished by testing your water for nitrates.

Your nitrate levels will rise every week when you keep your tank moderately full. When we track the rise in nitrates, we can adjust our tank. As an example, I am going to use an aquarium that produces 10ppm of nitrates per week. We want to keep nitrates under 40ppm, as we stated previously. In this example, we can see that after 4 weeks our aquarium hits 40ppm. We will need to do a water changing. We do a 30% water change. This will result in a 30% reduction of our nitrate levels. Our new nitrate number is 28ppm. We know that our fish will produce 10ppm of Nitrates in a week. This brings our total to 38ppm. As you can see, we will be changing our water every week in line with current trends.

I prefer to perform a 30% water change on my aquariums when it is time. While larger water changes might seem to be more beneficial, it can also cause stress to the fish and plants. Water changes are made to maintain fish health. If doing a large water change causes stress and illness, then it’s not completing our goal. You might think, “But, I don’t want to change the water every week.” Don’t worry, you can tune an aquarium to fit your needs.

By feeding less or keeping fewer fish, you can reduce the frequency of water changes. There is also the option of getting a larger aquarium. When you add more water volume to the same amount of fish, you’ll spread the waste out over more water, resulting in fewer parts per million. My last recommendation for combating water changes is to add live plants to your aquarium. As they grow they eat nitrates. Be careful not to fool yourself, most tanks will still need water changes even if you use all these techniques. It’s only a matter of how long between the water changes.

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