A properly maintained pool is one that is not only clean visually but biologically clean as well. If the chlorine and PH levels are maintained, bacteria and algae will be killed and the pool will be biologically safe. Filtration is mechanical process of removing insoluble matter from swimming pool water.Pool water carrying particulate matter, ‘solid and debris’ is passed through filtering media and then allows clear water to return to the pool. Water clarity is important for appearance, hygiene and safety.