I know some people on this forum have used water from a pond. I am not sure what you would have to do differently that to get get the water clean , because I never did it, I am afraid to encourage, or discourage it. In my opinion, cleaning up the water from a pond would be no different from cleaning up a pool that was left standing and turned green, except for the amonia that would be in the water from the fish - but I could be wrong. Maybe you could pm Waste - he is really good with the chemistry of water, and the organisms that can grow.