How to Remove Green Water

Green aquarium water is caused by microscopic algae that live suspended in the water. This form of algae lives off light and nutrients in the water. Green water is sometimes referred to as an algal bloom and is often caused by too much light, overfeeding the livestock and poor aquarium maintenance. Removing green water in the freshwater aquarium can be relatively simple, but it is important to find the cause of the algae in order to combat it long-term.

Things You'll Need

  • Liquid ammonia test kit
  • Liquid nitrite test kit
  • Liquid nitrate test kit
  • Green water removal chemicals
  • Ultra-violet (UV) filter
  • Diatom filter
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Instructions

    • 1

      Test your water for ammonia, nitrite and nitrate. Green water can be a sign of excess nutrients. Test your tap water for nitrate.

    • 2

      Do a 50 percent water change with fresh, temperature-matched, conditioned water if any ammonia or nitrite is detected. Repeat at 12-hour intervals. Use weekly partial water changes to keep nitrate no more than 10 ppm above your tap water level. If the green water does not clear up after a couple of weeks, proceed to Step 3.

    • 3

      Perform a 72-hour blackout on the tank. Reduce the the photo-period to 6 hours a day. Combine with large partial water changes.

    • 4

      Reduce the amount and frequency of feedings, and consider adding more live aquatic plants to the tank. This will reduce the excess nutrients available for the algae. If this does not improve the water, move to Step 5.

    • 5

      Purchase an algae removal chemical that will clump the algal spores together. This will enable them to be removed by the filter. Avoid any chemicals that contain herbicides or claim to "kill" the algae. Dose the anti-algae product according to the manufacturer's instructions, redosing as necessary to clear up the condition.

    • 6

      If none of the above steps work, consider installing a UV or diatom filter.