Abstract: The invention relates to a method for biological treatment of water in swimming pools. The method requires neither chlorine nor other toxic chemicals in the pool water, since near-surface pool water is mechanically purified in a first water circuit and suspended matter situated in the pool water is first retained in a biological filter (9) in a second water circuit and organic matter contained in said suspended matter, such as algae or detritus, and also organic matter dissolved in the pool water, are mineralized by the action of bacteria, wherein the phosphorus contained in the organic matter is catabolyzed to form dissolved reactive phosphate that is then bound by adsorption in an anion exchanger (14).

Abstract: The invention relates to a simple and environmentally friendly method to reduce the growth of algae in natural or artificially created bodies of water such as lakes, pools, ponds or swimming pools by the introduction of CO2. According to the invention the CO2 is obtained from air from the soil or from air from stacks of compost, with said air being mixed with the water to be treated.