Eco-Friendly Ways to Deal with Algae Problems in Saltwater Aquariums

Algae in a saltwater aquarium is both unpleasant-looking and unhealthy for your marine fish and plants. The leading causes of runaway algae in saltwater aquariums are phosphates, nitrates, too much dissolved organic material, and using aquarium lights for more than 9 hours a day. Learn these tips to deal with the causes of algae problems in your saltwater aquarium in an eco-friendly way.


Phosphates can get into your saltwater aquarium when you use straight tap water mixed with sea salts to form your saltwater environment. Purchase a reverse osmosis and deionization (RO/DI) water processor to filter and purify your tap water before putting it into your aquarium with the sea salt mixture. Once you have cleaned out the algae, use only RO/DI filtered water in your aquarium.


Excess nitrate in your saltwater aquarium is harmful to coral and other invertebrate life. Nitrates can build up in your saltwater from improperly purified fresh water. Check the sea salt mixture that you use, as well. If it has a high percentage of either ammonia or nitrogen, it will contribute nitrates to your saltwater that algae love to feed on. Another way to reduce nitrates in your saltwater aquarium is to plant mangrove plants near the aquarium filter and sump pump. If high nitrate levels persist in your aquarium, purchase a nitrogen-absorbing bacteria formulation from your pet store, to pull nitrogen out of the water and release it into the air as a gas.

Test Your Saltwater for Nitrates and Phosphates

Use a testing kit to test your saltwater weekly for the nitrate and phosphate levels in the water. Phosphate levels should be below 0.5 milligrams per liter (quart) range, and nitrates should be less than 10 milligrams per liter (quart). Perform the tests before and after you spot algae in your aquarium, to determine how much nitrate and phosphate the algae are actually consuming to fuel their growth.

Dissolved Organic Material

Among the easiest ways to control algae growth in a saltwater aquarium is to be stingy with powdered and flaked fish food. Follow the maximum feed levels diligently. Excess food matter in the water makes it cloudy, reducing the oxygen level for fish, but increasing the carbon dioxide level, which helps algae proliferate in your tank.

Other Solutions to Algae Buildup

Clean and refresh the salt water in your aquarium regularly, at least once every 2 months. Once you drain the aquarium, the algae will shrivel and turn into a jellylike material. You can then remove the algae from the glass with a spatula or large plastic spoon. While cleaning your aquarium is a tedious task, all the plant and animal life in your aquarium will benefit from the cleaner environment. If you follow the tips above to reduce nitrate and phosphate buildup, your aquarium will stay cleaner and free of algae longer. Reduce the number of hours that the aquarium light is on. While the aquarium is lit, the plant life, including algae, can conduct photosynthesis and grow out of control. Nine hours a day of light in the aquarium is a recommended maximum.