I've had a garden pond (150 gal) for 14 years. It has never had a filter in it. The fish seem to do well year round. On average, I probably replace the fish about every 3-4 years. I use goldfish since they are cheap. They start out as feeder size and have grown to about 4-5". After cleaning the pond this spring, I thought I'd try a homemade filter this summer. Other than the pump, I have about $30 into a "milk crate" filter. This site has been helpful with tutorials and ideas.