A filtration system will give you clear water and it will produce healthy water.
The filter's ultraviolet clarifier kills the algae that causes the water to go green, by disrupting its DNA. The filter bacteria help to neutralise bodily waste produced by fish. In this way, the filter stops the pond going green and allows you to feed the fish more often or to have more fish.
Many people choose undersized filter equipment with disappointing results. It is always good to install equipment that is equal to the demands of the pond, with plenty of spare capacity. Most filtration systems will consist of a pump, a biological filter box and an ultraviolet clarifier. The water garden filtration equipment will need to be maintained correctly if it is to work well.