How to Clear Green Aquarium Water

Powder Blue Tang

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.

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.

Leave a Reply

11 Comment threads
10 Thread replies
Most reacted comment
Hottest comment thread
13 Comment authors
Notify of

i have had a fish tank since i have been on my own and this is the first time i have ever had green water in my 55 gallon.going to try to use algone see if that works and cut the feeding to every other day and only what they can eat.what else should i do ?

I think that’s a good start. You can also increase the frequency of water changes to one every 3 – 4 days. But don’t change more than 15% at a time. Just do this temporarily while combating the green water. This should help speed nutrient reduction responsible for green water in your aquarium.

Sarah jones

My tank keeps staying green I do a water chanege every few days cleaned the stones fillers even got a new one keep light off for a week cut feeding to every ather day the water not clearing


With stone fillers you mean gravel? Feeding every other day is a start, make sure you feed no more then what the fish can eat within one minute. Water changes should not exceed 10% per week.
Other factors that are worth considering:
– plants, make sure they are doing well as they will otherwise contribute to a less than optimal water quality
– fish, green water will be more persistent if the tank is overstocked
– maintenance, make sure you keep up with general maintenance (water changes, gravel cleaning etc)
– aquarium additives (fertilizers, pH adjusters,bacterial supplements etc) can contribute to the green water


I cleaned my tank last night and my tank water is still green, could it be because i am over feeding?

Yes, overfeeding will introduce excess waste into the aquarium. We generally recommend feeding only once a day, and sparingly at that. When algae does break out, you can safely feed once every other day in order to reduce organic waste. Fish have a very slow metabolism, so it is perfectly safe to feed every other day. Most fish will also graze on whatever they can find in the aquarium… such as food particles settled on the gravel and algae growing on rocks and ornaments. Lastly, when your aquarium water turns green, do not do a thorough cleaning of the aquarium… Read more »


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


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.

Angel Massie Roberts

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

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… Read more »


What are nitrates

Go here to read more about nitrates, and check out this article too. Also check out our article about the nitrogen cycle for a better understanding of nitrate in the aquarium.


My fish tank is green, not the water, what can i do so my fish tank don’t turn green any more.

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… Read more »

judy schuster

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


The article above is a quick reference. We have a much more detailed article available at If you have any questions, please contact us through email, or call our customer service team.


It is not uncommon for a tank with algae to test low for nitrates. The nitrates are being used as a food source for the algae.

Give done everything. To clear green cloudy water and sometimes. It’ll. Clear up some and now its being a pain and wnt. Need help w this one.

Algone is an effective aquarium water clarifier and nitrate remover. To learn more and purchase go here.

Thilo @ Algone

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.

Habib. m.s

But which is the best chemical to be added into the aquarium to maintain a good health for Fish

Click to Hide Advanced Floating Content
Cart Menu Button Image0
Your Cart