The turbidity of water refers to the presence of suspended matter - either living
organisms forming plankton (rare in an aquarium) or inert matter, such as animal
or vegetable remains or particles of sediment, particularly mud.
The size of this suspended matter ranges from a few thousandths of a millimeter
to several millimeters. In calm, unstirred water it forms sediment at a speed in
proportion to its weight. In running or turbulent water, some of the matter remains
permanently suspended, giving rise to more pronounced turbidity.
In aquariums, where the water is always in motion, systems of varying degrees
of sophistication (see Filtration, page 237) allow fishkeepers keep their water
The effects of this are entirely positive:
- the visual appearance is improved;
- the light required by the plants penetrates the water and reaches them more
- there is less risk of disease, particularly in the fishes' branchiae;
- there is little sedimentation on the base of the tank, reducing both the
possibility of any warping due to excessive weight and the decomposition of