OASE Germany have developed a number of treatments to help reduce phosphate levels in fish ponds and swimming ponds, thus greatly limiting single-celled, filamentous and slime algae growth. PhosLess Direct can be directly applied to the pond water and will bind excess levels of phosphates. The new PhosLess Flow and PhosLess Power Flow are cartridge filters which can be connected to a flexible hose after the pond filter and the specially developed media inside the cartridge will initially reduce phosphate levels by binding this within the media and then maintain this low level over time.
Products such as the Norit Activated Carbon can be used to bind tannins which can occur during the decomposition of leaves and organic matter or if non-aqueous planting soil is accidentally used. Tannin causes the water to stain brown or yellow and can very difficult to remove, similar to a tea bag in warm water. Your pond filter cannot extract the tannin from solution and water changes may have little effect unless this is considerable. Activated charcoal can be bagged and placed in flowing water from the filter return or fitted inside the filter system itself and will help to bind the tannin staining and greatly improve water clarity.