Green Aquarium Water

Green aquarium water often results from allow in too much light. The only light that should be directed into the tank should be artificial and controlled.

It is not a good idea to leave the light running all the time. It should be turned on and off to simulate, as much as possible, the natural daylight and nighttime periods. Too much time using a good spectrum for plant growth will promote plants, but they should be given rest periods.


If sunlight is allowed to enter the system, it is a powerful engine for the growth of algae. There are quite a number of algae strains. At their most basic they are single celled plants.

These either are suspended in the water or attach to surfaces in the aquarium. In the presence of both sunlight for power and an abundance of dissolved nutrients the population explodes.

Green aquarium water occurs where this dense population of algae is so thick it can turn an aquarium's water into a thick pea soup appearance.

Green aquarium water is extremely hard to eliminate once it has gotten a foothold. Since these are single celled plants, they are often so small that they will pass through the filter and not be trapped.

There is no algaecide I would recommend to kill it, since it can cause stress to the fish and harm to other plant species. The only remedies on the market that might be of use would be various flocculates.

These products will cause the algae to clump together so that they can be trapped in the filter. The clumps are messy and quite gooey. I would suggest not using the standard media when a flocculate is used. Replace the media with Poly Wool .

This is an extremely cheap media and gets clogged quite rapidly. The mess will need to be removed after less than a day and should reduce somewhat the density. It rarely removes all the cells.

The remaining algae cells will immediately begin to multiply once again if the advantageous conditions remain.

The problem with this type of treatment is that you can't use it over and over. Overdosing will quite rapidly cause the reverse reaction to occur and the tank will get worse.

The only effective way I know to remove the cause of the green aquarium water problem, the algae cells themselves, is with a Diatom filter. The very best is from Vortex Innerspace Products.

These units are quite expensive, but they are the best mechanical filters I have ever seen. I have used them to remove clouds of all kinds. The sieve they produce uses diatoms.

Diatomaceous earth will capture the single cell against the powdered bag. It may take some time for the green aquarium water cloud to return, but if the original causes still remain, they most certainly will.

The sun is the major cause

It is the sun that is the main culprit. Very good artificial lighting that is left on for extended periods of time may be a cause occasionally. However, in almost all cases, the sun striking the tank sometime during the day is the cause.

The tank should be located in a place where it is not touched by the sun. If the room is extremely bright, it also is best to drop the curtains when the sun is out and brightening the room.

An aquarium background is important in preventing any natural sunlight from striking the aquarium during the day. It should be used if the sun is striking the aquarium from the back especially.

If the tank is situated such that the sun comes in through the side, it is possible to wrap the background around the side as well. This may remove a side from viewing, but the green aquarium water pretty much does that when it is allowed to occur anyway

Phosphate is a limiting factor

A second contributing factor is a high concentration of phosphate in the water. Phosphate is the only part of fertilizer that can be controlled.

The other components, such as nitrogen and potassium are so bountiful they cannot be controlled or removed from the system.

Phosphate is a limiting factor, if there is enough of it, the bloom can occur, if there is not enough, the algae cannot explode readily.

There are a number of ways to try to control phosphate:

  • Limiting feeding is one.
  • Using a low phosphate food is another.
  • Finally there are phosphate resins that can remove it as part of the filter media.

It is impossible to remove all the phosphate from the system.

The real goal is to remove enough that the algae are deprived of enough to explode, even in the presence of light.

If there are any rooted plants, these requires some as well. Actually rooted plants are better able to compete for limited amounts of phosphate.

They will often get it before the algae can. This deprivation prevents the algae from getting a momentum going and stops the bloom from occurring.

It is best to combine both approaches to prevent green water. It is worth it. Anyone who has experience it knows how difficult it is to eradicate once it has gained a foothold.

If the problem persists, you might have to find a Diatom filter to remove the algae mechanically

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