QA - Here are some thoughts just from high level. You aren't running 24/7 to avoid raising the temp to a level that stresses fish. However, if the DO gets much lower you possibly risk fish dying. I think bump up the run time and gather more data. It really seems like the only short term option to me. Long term option - what about installing a bigger pump to get even more turns per run time? It would seem that if you exposed the water to atmosphere even more it would have no choice but to absorb more O2. If you could do that in the same run time you are doing now then you shouldn't have to worry about temp.
