Algae in your Freshwater Aquarium

by Susan Horton, DVM

What is Algae?Algae should be thought of as a type of simple plant that develops when water and light are present. Algae is not harmful to an aquarium but in most cases is considered unsightly and customers want to control or eliminate it. What causes Algae to grow? For algae to grow it needs light. Both the aquarium and room light can cause algae to grow. If your tank is getting more than 10 hours of light a day you may notice green algae starting to grow. Warm water and ‘nitrates’ (which build up from not doing regular water changes) will cause algae to grow quickly. Also if phosphates are present, they will promote algae growth. How to control Algae:

  1. Control the light received by the aquarium. The less light your tank gets, the less likely it is you will have algae.  Do not place your tank where direct sun light will affect the tank.  Keep your aquarium lights on a timer and limit the light to 10 hours a day.
  2. Regular water changes.   We recommend a 1/3 water change every 2 weeks for an established fish tank.  Algae uses excess fish food and fish waste for fertilizer. By doing regular water changes you will reduce the amount of “food” the algae has.
  3. Live plants fight Algae.  They compete for the same nutrients.
  4. Certain fish are “Algae Eaters” and will naturally help control algae growth.
  5. Many chemicals are available to help algae from growing. These chemicals are “inhibitors” and will prevent some algae from starting to grow but will not get rid of Algae after it has started.  We prefer a more natural tank without these chemicals and therefore do not recommend them.
  6. You may want to purchase a scraper or pad to remove algae from the sides of the aquarium. Don’t use anything from the supermarket to clean your tank, as it may contain soap which is deadly to fish!

Algae blooms or green water problems An algae bloom is a suspended algae that makes the water green but does not grow on glass or ornaments. If this happens to your tank the best way to get rid of it is by ‘starving’ the Algae. Cover the tank with newspaper so it is completely dark for 48 hours (during this time only feed every other day). This will cause the algae to die. After 48 hours, do a 1/3 water change. In some cases the water change may have to be repeated. Green Algae is caused by too much light.

  • Reduce the amount of light
  • Do regular water changes
  • Don’t overfeed
  • Get algae eating fish

And you will control this problem.


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