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

We hobbyists need to perform water changes often in order to mimic nature. Most waterways have very low nitrates in the water because wastes are constantly being flushed downstream. Unfortunately, nitrates is the side effect of feeding fish. 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. It is easy to change water. We want to remove water with nitrates and replace it by water that doesn’t. I want to be able to control the water quality. 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. You can also find discus breeders that do it every day! Who is right?

They are all right and all wrong at the same time. They are correct that they have a schedule that works for them. However, they are wrong in recommending a specific water change schedule. It is better to show the individual how to assess their water changing requirements. First we need to realize that every tank will have a different water change schedule. This is because each tank will have a different bio-load. How much fish is consumed and how many meals are taken is what determines the bio-load. It doesn’t take much thought to realize that more fish combined with more food will result in more fish waste. Conversely, less fish and food would result in less waste. This is how we can determine how much waste our produce. Test your water for nitrates to find out how you can measure it.

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 we have stated, we want to keep the nitrates at 40ppm. In this example, we can see that after 4 weeks our aquarium hits 40ppm. We need to perform a water change. We conduct a 30% water exchange. This will decrease our nitrates 30%. Our new nitrate number is 28ppm. Our fish will have 10ppm of the nitrates within a week. Our count will now be at 38ppm. We can see here that with the current trends, we’ll be doing a water change every week.

I prefer to perform a 30% water change on my aquariums when it is time. Although larger water changes may seem better, drastic water changes can cause stress to plants and fish. Water changes are made to maintain fish health. If large water changes cause stress or illness, we have not achieved 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. If you have more fish than water volume, the waste will be spread over more water. That means less parts per million. My last recommendation for combating water changes is to add live plants to your aquarium. They eat nitrates as they grow. Don’t be fooled, even with all the above techniques, tanks still require water changes. It doesn’t matter how often you wait between water changes.

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