Filtration is a key process in fish keeping be it a Bowl / Glass Tank or Outdoor pond or pool. Fish will have a healthy life only in clean and aerated water. In the natural environment like River and lakes, the water is renewed automatically. The Nature does the water cycle by itself. Yes of course humans pollute it most often. We will talk about aeration in the a different thread. For now let’s stick to Filtration. Biological filtration is the best suited method for fish ponds. In a captive fish pond the ecosystem is closed and hence the water cycle will not happen by itself. Any kind of impurity generated inside or induced from outside needs to be cleared by force. So there are two parts of clearing these impurities. Have a good Filter system Partial or full Water change (Need based) Selecting a Filter System There is a myth that green water in the pond is not good. Or the Black bottom of the pond means its water is not good. Reality is that some algae in pond...