Eco-sytem  

People do not  want to invest in a pond that is going to turn green and look like a swamp. Keeping a pond clean, clear and beautiful is not hard if you understand how a ecosystem works. First, if anyone tells you all you need are plants & a filter to keep a pond clean doesn't understand how pond ecology functions (or they are trying to sell you something). To keep water clear you need a mechanical and biological filter, plants, fish and bacteria. Taking any of these elements out causes the ecosystem to work less effectively and conditions the water to promote algae growth. A well balanced pond combining all of these factors should never go through a "green phase". Never, ever use chemicals to kill algae. Chemicals will kill algae, but can also destroy the ecosystem thus creating a lot more problems in the long run. A well-designed pond is a balance of filters, plants, and bacteria all working together.