How to clear green aquarium water

Powder Blue Tang
(Last Updated On: March 12, 2017)

Step one: Keep your cool!

Once fish disappear in green water, we often act with a sense of urgency. We tend to overcompensate with large water changes and other big ideas. In most cases sudden BIG CHANGES in the aquarium have negative consequences.

The larger the change, the greater the resulting biological imbalance.

Small, gradual actions allow for the fish tank to adjust more quickly to the biological changes.

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The most immediate threat of green water is oxygen depletion. Green water is a free-floating algae bloom and algae takes up oxygen just like any other plant. Creating surface agitation in the aquarium can easily increase oxygen levels. Adjusting the filter return to increase surface water movement will increase available oxygen in the tank. Further, the tank temperature can be lowered a few degrees increasing the water’s capacity to hold oxygen.

Follow these steps to clear green aquarium water:

  • Keep water changes at about 15 – 20% every other week.
  • Remove waste from the tank with an aquarium siphon.
  • Remove nitrates, as this is the primary food source for algae.
  • Cut feeding to once every other day. Don’t feed more then the fish can eat within about one minute.
  • Decrease the lighting period to no more then 6 hours per day.

Following the steps above will put your aquarium on a path to recovery.

Preventing green water:

Once the tank has cleared up future green water outbreaks can be avoided by limiting the amount of waste in the aquarium and keeping nitrates as low as possible.

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14 thoughts on “How to clear green aquarium water

  1. Elaine says:

    Hi I have only had my tank 12 weeks just get the tank spot on and this green water appeared I am getting new filter with u v in it with that make differance and do I need to clean tank right out stones and everything else that’s in tank I have added green away yesterday dosent seem to have done anything thank you

    • Thilo
      Thilo says:

      Not uncommon when you start a new aquarium, waste accumulates, setting the table for all kind of issues. Algone will assist in reducing waste, reduced feeding, increased aeration will do the rest. Refrain from large water changes, little but more frequent is better.

  2. Angel Massie Roberts says:

    I have just started to have this problem,, green cloudy water!!! Done water changes and it still keeps happening,, what can I do to get this under control and kepp it maintained so it does not keep happening?? Does anyone know or have any advise on this issue?? I look forward to hearing from anyone. Sincerely nd Thank you,, Angel M. Roberts

    • Scott @ Algone
      Scott @ Algone says:

      Hi Angel! A couple of things worth checking into and assessing regarding your cloudy green water:

    • Test for nitrates. Nitrates are the primary cause for green aquarium water (which is a free floating algae bloom). Rising nitrate is the result of accumulating organic waste in the tank. To avoid unnecessary waste, make sure you are not overfeeding your fish. You can safely feed once every other day. This will go a long way in clearing up the aquarium.
    • Make sure your tank is not over-stocked. Too many fish in the aquarium will cause problems. Again, the aquariums ability to sustain healthy fish life will be pushed to its limits due to excessive organic waste for the tank volume. Our recommendation is 1 inch of fish per 2 gallons of water.
    • Limit light. Make sure the tank isn’t placed in direct sunlight for any extended periods of time each day. Further, unless you have a reef or planted aquarium that requires a lot of light, consider lighting only for a few hours per day. Choose a time when you are home and can enjoy the tank. In nature, most fish live in subdued lighting. Light is primarily for the benefit of the aquarium owner. Too much light will cause excessive algae growth or green water if conditions are right.
    • Do not go overboard with water changes. It can be tempting to change too much water, too frequently when experiencing green aquarium water. This however can make a bad situation worse. Changing too much water can disturb the beneficial bacteria in the tank which is need to balance the water.
    • Lastly, consider the use of Algone. Algone is an excellent aquarium water clarifier and nitrate remover. Algone helps balance the water and make it safe for healthy fish life.
    • I hope this helps. Happy New Year!

    • Scott @ Algone
      Scott @ Algone says:

      The cause of green aquarium water and algae growing in the fish tank are the same. High nutrients are generally to blame. You should make sure nitrate is low as this is a primary food source for algae. Nitrates are the direct result of decaying organic waste in the tank. Usually this is food either uneaten left to decay, or fish excrement. Either way, it’s generally good practice to feed a maximum of once per day sparingly. It’s also perfectly fine to feed once every other day while trying to clear the aquarium. Fish have a very slow digestive system and will do well on the reduced amount of food.

  3. judy schuster says:

    We have done everything that u suggest to clear the green water….have taken water samples to pet store and they tell us our water tests perfect….this has been going on for 3 months…help!!!! Thank you

  4. Thilo @ Algone
    Thilo @ Algone says:

    The best chemical to maintain good health is probably the ones that prevent issues. The term chemical of course used loosely here, but activated carbon, water conditioners, and products like Algone, literally anything that removes waste and pollutants.

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