The house I just bought has a pretty good-sized concrete pond, complete with stone bridge over it, that I suspect was once a koi pond. Now it is just covered with green algae (duck grass?), but the frogs seem to like it. There are at least 6 frogs floating around just barely underwater, so that tells me the water is still pure (aren't frogs really sensitive to pollution, etc.?) (Yes, the floating frogs are alive!)
It has a pump setup that seems to work through a bucket lined with a ball of metal mesh (sounds similar to Jason's well pump installation he recently described). I think the mesh is probably just to keep the pump intake pipes clear.
Any suggestions for the best way of reviving the pond (without draining it and leaving the frogs and any fish that might be hiding high and dry) ? I'm not really sure where to start, except maybe by skimming off the algae/duck grass, but seems like there's probably alot more than that to reviving it. I wouldn't mind restocking it with koi (although not sure of the cost of doing so).