I'm just curious if other people out there keep their ponds natural. I've had a pond for 19 years and I've never had a filter, never tested the water and have healthy fish that breed and never seem to die. I do run a waterfall in warm weather and an aerator in cold weather. Anyone else?
I think this has a whole lot to do with your local water quality. Here the water is too alkaline, but I believe where the water is softer you have a lot more acids to help break down organic compounds that would normally pollute the water.