The title links to a good overview article on natural swimming pool where plants act as filter to keep water in the pool clean and healthy without any need of chemical.
Some keys points:
- reserve 50% of the pool surface for plants - this is not necessary bad because the plants themselves are beautiful and are part of your backyard/swimming pool.
- the plant area should be shallow, starts at 15cm (6 inches) from the edge to about 45cm near the swimming area. The plant area is separated from the swimming area by boundaries with about 2cm (less then 1 inch) clearence at the top to allow free water flow between plant area and swimming area. Additional benefit of the shallow part is the heating effect. It helps to keep the water warmer.
- circulate the water from the swimming area to the plant area for cleansing using water pump. [Some design recommends that the plant area is complete separated from the swimming area at the top and leave tunnels for water to go back to the swimming area near the bottom of the pool and circulate the water use water pump solely.]
- aerate the water, either using water falls or air pump(s) which deliver bubbles in the swimming area.
- monitor the health of your water by allowing frogs to breed - they also eat mosiquitos! If the frogs disappear, your pool is in trouble!