Fish pollute pond water through their metabolic waste. Pond fish, koi in particular, require a clean living environment conditions and so are their own worst enemies because of the waste they produce. If you have pond stocked with fish you want to keep healthy filters, ultraviolet sterilizers and skimmers are available to help rid the pond of material liable to harm its inhabitants. Pond filters should incorporate mechanical, biological and chemical filter compartments. An ultraviolet sterilizer is valuable when pond water turns green from excessive unicellular algae. Skimmers are used on overstocked ponds to increase oxygen levels and to reduce the protein levels.
Place the filter box at the highest point of the pond.
Remove the filter box lid and fill the compartment furthest from the intake point, which is the biological filter area, with biological material, such as bio-balls.
Fill the filter compartment into which the pond water flows, with filter matting. This material acts as a mechanical filter. The matting physically traps detritus and debris and thereby removes this material from the pond water.
Rinse the filter matting on a weekly basis once the filter box is operational.
Place a nylon bag of activated carbon into the middle compartment of the filter box. Remove this bag after a week. Use activated carbon for a week each month, once the filter is operational. The carbon traps molecules of waste within the pore of its structure, but will leach this waste back into the water, once it becomes exhausted. Discard and replace the carbon every four weeks.
Place one end of a 4-foot piece of plastic tubing over the exhaust nozzle of the submersible pump and position the pump on two bricks or flat stones, on the bottom of the pond. The pump is elevated slightly off the bottom of the pond, to prevent it from drawing in sludge that slowly accumulates on that area.
Push the opposite end of the tubing over the intake nozzle of the ultraviolet sterilizer and place the sterilizer on the ground, next to the pond. Disguise the sterilizer by planting shrubs or other plants around it, once the filter system is operational.
Place one end of the second 4-foot long piece of plastic tubing over the exhaust nozzle of the sterilizer.
Place the opposite end of the plastic tubing, onto the inlet nozzle of the box filter.
Place a second submersible pump in the pond and attach this via your third piece of plastic tubing, to a skimmer, which is positioned in the water.