How to Culture Greenwater

Last Updated: October 21, 2021 References

Greenwater, or phytoplankton, are known by most aquarium hobbyists as good quality small fish fry food, like betta fry. This article will outline some of the ways you can make your own.

Method 1

Method 1 of 2:

Simpler, slower method

1
Put aged aquarium water in a clear container.^{[1]
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Expose the water to the sun. Doing this takes quite a long time for the algae to bloom.^{[2]
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Research source} See the next method for something faster.

Method 2

Method 2 of 2:

Faster method

1
Pluck 10 smoothly surfaced and thin leaves.
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Wash and rinse the leaves until they are clean. Don't use soap!
3
Put the leaves in the blender with water. You can also add fish micro pellets to help the culture bloom more quickly.
4
Blend the water with the leaves. Do this for about 1 minute.
5
Sieve any blended leaves and put the water in a bottle.
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Put the bottle under a bright light overnight so that the phytoplankton will bloom.
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Fill a bucket with water.
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Put the greenwater that has been sitting under a bright light overnight in the bucket.
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Let the bucket sit under the sun. In about a few days, the phytoplankton will grow.

Community Q&A

Question

Even after sieving all the leaves out, it is okay for the green water to have a thick, more green sediment at the bottom and the top to clear up a little and become less green?

Community Answer

Yes, this is probably common as some of the blended leaves will be in pieces that are too small for a simple filtering material. If you want to filter as much as possible I suggest something like nylon stocking material. It tends to filter better than cheese cloth and you can get it for $1 at a dollar store. I use them as a mechanical filter for my 55gal tank.
Question

The green water in one of my plastic buckets turned red, why?

Community Answer

There are many types of algae, blue, green, and the most primitive type are red. I am assuming that somehow red algae spores got into your greenwater culture, and took over.
Question

I had fish poop from another aquarium I wanted to use for watering the plants, but the water turned green in a few days. Is that green water safe for feeding?

Community Answer

Yes, it is. You'll get an added benefits from the algae and other microorganisms that are in the green water.

Warnings

Do not feed the fresh blended greenwater straight to your fry! Let it sit under the light so the phytoplankton will grow and all of the cells in the leaves died first. Some cells in the leaves are the defense system of the plant and this can kill your fry.

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