Mike,
Since the fish are piping, you know O2 is low.
Before we can help eliminate the problem, we need more information.
Hows the biomass? Too many fish can cause this problem. Too much vegetation can make it worse.
How deep is the pond? Do you know the water temp? Have you checked the chemistry?
All these things and more can contribute to your problem. The quickest fix is to reduce the fish load. This will give you time to figure out the rest of your problems.
