Aquarium Water Clarity

by Tony
(Sedgwick, Ks)

What do I need to do to clear the water up in the aquarium? It is slightly hazy.

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Grant's Reply


Hi Tony

Hazy water is very frustrating when you see other aquarium setups with perfectly clear water.

You don't mention whether you have a filter, so I assume you do otherwise you would just replace the water when it became hazy.
The three main causes of water clarity issues are:

1. Sediment
2. Bacterial
3. Algae

Sediment is a problem for new setups when clay has been mixed in with the substrate and it hasn't been removed properly during cleaning.

Any organic material left after cleaning usually breaks down quickly and is handled by the filter. Clay unfortunately doesn't break down and so floats in suspension. The particles are too small for the filter to remove unless you go to extreme filtration such as a Diatom filter.

The solution is to replace all the water, which may take a couple of changes before all the clay is removed, or completely break down the setup and clean the substrate properly.

Bacterial blooms are normally associated with new set ups.
As the new set up goes through its first biological cycle and the filter establishes a bacterial colony, bacteria tend to bloom until after a few days the majority die off and the water becomes clear.

The solution is do nothing, and let the bacterial bloom die off naturally.

The most likely cause of hazy water is an alga bloom.

Algae cause a slightly green haze which gets progressively thicker the longer it is left.
Filters cannot filter algae from water, despite most hobbyists thinking they can. The alga are too small.

Filters take out very little water contaminants mechanically. They take out contaminants by bacterial action. In other words the bacteria eat the waste.

Alga need two things to flourish:
1. Light
2. Nutrients

This is the never ending battle for aquarists, getting the balance right so the alga don't have ideal conditions to flourish by minimizing either or both.
The rules for aquarium location are:
1. Do not place it where it will receive direct sunlight.
2. Do not place it near any source of indirect sunlight.
3. Do not place it near any source of strong direct or indirect artificial light.

Light is everything in controlling alga. A well established aquarium will still get some spot algae on the sides. Aquariums that are getting too much light or too many nutrients in the water or both, will get the water turning green.

Check your nitrate level with a water test kit, it should be no more than 20-30 ppm (parts per million). If the nitrate readings are too high, you aren't doing enough partial water changes.
Read more on aquarium setups.

If the readings are within the acceptable range, you have too much light reaching the aquarium.

Once you have your balance right, activated charcoal is good for "polishing" the water.