Behind every clear water pond is an effective filtration system. Filters collect debris and fish waste, keeping it out of the pond and away from the algae and filters also give nitrifying bacteria more surface area on which to grow which also helps to control algae. They can cost anywhere from $75 for a small
do-it-yourself filter to many thousands of dollars for large ponds. If you are having problems with green water or string algae you probably have an under sized filter or no filter at all. . Filters for small ponds can be in ponds, but ponds over 500 gallons require more surface area than you want taken up in a pond and so they should be an out of pond filter. There are two parts to filtration. Mechanical filtration and biological filtration. Each serves as an important part of keeping your pond clear and healthy.
A do-it-yourself filter - 30 gallon tote using
scrubbing pads, cleans a 500 gallon pond.
Amount of debris a mechanical filter
picks up in 2 weeks in a clean pond.
Drum filters clean very fine particles from the water and are self cleaning
UV filtration passes water around a bright fluorescent UV tube housed in a pipe to kill floating bacteria that make water look green. This filter will not kill string algae and will not harm fish or plants in the pond. While the light may glow, the intensity drops after two years and the tube should be replaced. If you have kept the organics out of your pond and your pond is still green this filter may be a good option in helping keep your pond clear.
Mike Bentley has complied a list of different people who have shared their ways of making homemade filters. It can be found by clicking this link.