You're in a tough spot with a community pond. I would imagine that draining and starting over is probably off the table, and I'm guessing you are probably limited to working with what you currently have. If that be the case, you could try adding some LMB to work on the small gills and bullheads. If it were me, I wouldn't get too carried away with adding fish until I was more confident of their long-term survival, however. Be a shame to lose what you've added due to low O2, and/or poor water quality.
