How often should I change my water?

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Why are water changes required on an aquarium? How often should I change my water and how much should I change each time I maintain my dirty tank?

About 25% once a week works well for most people, but it really depends on your tank.

Water changes are primarily for controlling nitrate, which rises over time and can lead to algae problems and poor fish health.

It can also result in losses when new fish are added.

When you do a water change dirty nitrate-laden water is removed from the tank, using a gravel-cleaning syphon, and the tank is topped up with tapwater that is lower in nitrate. This dilutes the nitrate level in the aquarium and helps keep the tank and fish in good shape.

However, nitrate is produced constantly and the rate at which levels rise will depend on the tank volume, number and size of fish and what and how much they are fed. Your water change regime needs to be sufficient to allow for the nitrate accumulating between water changes.

There’s a simple way to tell if you are doing enough water changes. Test the nitrate level of your tank and then compare it to the nitrate level of your tapwater. If you’re doing enough water changes the two should be about the same. If you’re not, they’ll be far apart. A difference of more than 40ppm means you need to change more water more often.

This item was first published in the September 2009 issue of Practical Fishkeeping magazine. It may not be reproduced without written permission.