I have a pond that has been in place since 1996 stocked with Bass and Bluegill. With an open loop system the water does get circulated around (to some degree)and I do see bubbles from the geothermal return line. The fish have been in place for nearly 20 yrs and have survived. However, the reason for my question is I have lost just enough fish to make me wonder if aeration is necessary. In all I would say I have lost 20 or so bluegill and 3 smaller largemouth this year. All signs point to oxygen depletion: Carp lapping at top of water and fish being lost early in the AM and being found in the morning. My concern is will an aerator pump kill the efficiency of the geothermal and/or cause things to get stirred up and stuck in the intake? Any advice from others with an open loop system would be greatly appreciated. I have owned the property for a little over a year.