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Algae growth in an aquarium is indicative of high nitrate levels. Nitrates are the final stage of the nitrogen cycle - a bacterial process which naturally detoxifies the water in your aquarium.

A properly balanced and cycled aquarium will contain two types of bacteria - one which feeds on the highly toxic ammonia in your fish's wastes and converts it into nitrites, the other that feeds on the nitrites and converts them into nitrates.

Nitrates are far less toxic to your fish, but they are food for algae. There are chemicals that you can add to your aquarium to reduce nitrate levels. They contain other compounds, usually sulfur, that trap the nitrates in another form. This should only be considered, though, as a temporary "emergency" solution.

The fact is, anything you add to your tank water will remain there until you remove it. Even "harmless" chemicals can build up to harmful levels, changing the pH of the water, affecting your fishes' feeding habits, and reducing the amount of oxygen they can extract from the water.

The long-term solution to sustaining a healthy environment in your aquarium is to change the water regularly. You should buy a test kit to determine how often to change the water in your aquarium. Depending on the size of the tank, number and type of fish, type of food, etc. you may need to change the water weekly, or you might be able to get away with monthly.

When changing water, never change more than one half of your tank's volume at one time. Be sure to add the proper amount of chemicals (dechlorinaters, buffers, salt, clarifiers, etc.) and nutrients (vitamins, mineral supplements, etc.) for the amount of water you are replacing. Also be sure the water you are adding is close to the temperature of the water already in the tank to keep from shocking the fish.

If you feel you absolutely must use chemicals to prevent algae from growing in your aquarium, consider using any of the commercially available additives that contain copper sulfate. And most importantly, follow the directions!

Yes, copper salts are toxic, but that actually is good in this case. You only need a very small amount to keep algae and even protozoan parasites in check. In low concentrations, copper sulfate is very safe for fish because they are relatively large. In fact, copper sulfate is added to your city's drinking water to kill algae. And if you have copper pipes in your home, your water picks up additional copper ions from them, too.

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