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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. When this parameter is kept low, fish will be at their healthiest.

Generally below 40 parts per million is considered safe for most fish. A simple way to regulate this is by changing water. The act of changing water is as simple as it sounds. We want to take water out that has nitrates in it and replace it with water that does not. I'd like to focus on how to regulate the water quality. Most hobbyists simply change water at a specific interval. Often times you'll hear, “change your water every month.” Then there are those guys who say to do it every week. There are also those weird discus breeders who do it every day! Who is right?

They are all right and all wrong at the same time. They are right in that, the schedule they are using works for them. All of them are also wrong for recommending a certain water change schedule. A better method is to teach the person how to evaluate their water changing needs. 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. The amount of fish combined with how much food is fed is how you determine 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. We need to figure out how much waste we're producing. This can be accomplished by testing your water for nitrates with aquarium test strips.

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 need to perform a water change. We perform a 30% water change. This will reduce our nitrates by 30%. Our new nitrate count is 28ppm. As we know, in another week, our fish will have produced 10ppm of nitrates. Bringing our count back up to 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. Larger water changes seem like they would be better, however, you can bring on a lot of stress to fish and plants with drastic water changes. The goal of changing water is to keep the fish healthy. If doing a large water change causes stress and illness, then it's not completing our goal. You might be thinking, but I don't want to change water 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. 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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