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Urmston Aquatics, 20 The Circle, Barton Road, Lostock, Manchester, M32 9TR

Phosphates, Green Water and Cloudy Water

PHOSPHATES are one of the primary contributors to the growth of algae in an aquarium, both as algae blooms causing green water, and as algae growing on the glass & ornaments. High levels of phosphates may also lead to newly introduced fish suffering from shock, resulting in disease and death. Phosphates are introduced into an aquarium in many ways, tap water being a major contributor. Other sources of phosphate include pH buffers, carbon, salt, fish food & overfeeding, Phosphates can also be generated within an aquarium through a heavy fish load, wasted fish food, and also algae or plants which have died.

If phosphates are a problem the source must be found. In most cases this is either tap water or food debris in the gravel or filter. A phosphate test of your tap water will indicate whether the problem is caused from within the aquarium or not. If tap water is the source of the problem then the phosphates should be removed before the tap water is used in the aquarium. This can be achieved by using Reverse Osmosis water (using an RO unit), bottled water, or tap water which has been passed through a phosphate removing resin (eg. Rowaphos).

Cloudy Water


Cloudy water is caused by a bacterial bloom in the aquarium. A bacterial bloom is when the bacteria in the tank multiplies in such high numbers that they cloud the water. Bacterial blooms are caused by excess nutrients in the water.

This can happen when:
1) A tank is first set up.

2) New fish have been added to the tank.

3) After a water change.

4) Continuous over feeding.

5) Replacing or cleaning a filter.

The bacterial bloom itself is not harmful to fish, but the increased amount of bacteria will use vast amounts of oxygen, and may suffocate the fish. When a bacterial bloom occurs, fish are quite often seen at the surface of the aquarium gasping for air.


If left alone the cloudiness will go away, though this can take anywhere from a few days to a month. Control of the amount of nutrients in the water will keep the water clear, and this is easily done with regular water changes. If the problem water originated with excess food, then a 50% water change will have to be carried out, & all the uneaten food removed.

The water change may have to be repeated 2 or 3 times. The regular use of a bacterial supplement (such as Stress Zyme) will prevent a bacterial bloom. Chemicals are available which quickly remove the bloom from the water. These are fast working and are not harmful to fish or plants. Filter Aid and Accu Clear are good remedies.