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

To mimic nature, we as hobbyists many times, need to do water changes. Most waterways have very low nitrates in the water because wastes are constantly being flushed downstream. Unfortunately for us, the byproduct of feeding our fish is nitrates. This parameter should be kept at a minimum to ensure fish are healthy.

Generally below 40 parts per million is considered safe for most fish. This can be easily controlled by changing the water. The act of changing water can be as easy as it sounds. We want to remove water with nitrates and replace it by water that doesn’t. I would like to concentrate on water quality regulation. Most hobbyists simply change water at a specific interval. You’ll often hear hobbyists say, “change your water every other month.” But there are also those who insist on changing it every week. There are also those weird discus breeders who 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. However, they are wrong in recommending a specific water change schedule. A better method is to teach the person how to evaluate their water changing needs. We must first realize that each tank has a unique water changing schedule. Because each tank has a different bioload, this is important. The bio-load is determined by the amount of fish and food consumed. It is not difficult to see that more fish and more food equals more fish waste. Conversely, less fish and food would result in less waste. It is important to determine how much waste we produce. You can do this by checking your water for nitrates.

With a moderately heavy stocked tank, you will see your nitrates are climbing each week. Once we can track how our nitrates are rising, we can start to regulate it. As an example, I am going to use an aquarium that produces 10ppm of nitrates per week. As stated earlier, we want to keep nitrates below 40ppm. In this example, we can see that after 4 weeks our aquarium hits 40ppm. We must perform a water change. We perform a 30% water change. This will decrease our nitrates 30%. The new nitrate level is now 28ppm. As we know, in another week, our fish will have produced 10ppm of nitrates. 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. The goal of changing water is to keep the fish healthy. If large water changes cause stress or illness, we have not achieved our goal. You may be thinking, “But I don’t want water changed every week.” Don’t worry, you can tune an aquarium to fit your needs.

You can help combat the need for water changes by feeding less, or simply keeping less fish. There is also the option of getting a larger aquarium. You can increase the water volume for the same number of fish. This will spread the waste over more water. The result is a lower parts per million. My last recommendation for combating water changes is to add live plants to your aquarium. They eat nitrates as they grow. Be careful not to fool yourself, most tanks will still need water changes even if you use all these techniques. It doesn’t matter how often you wait between water changes.

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