I'm trying to figure out the right temp for my fish. For a while it was at 80/82+, but I was afraid the fish weren't getting enough oxygen, so I'm trying to maintain it at 78. I have a separate thermometer for the temp but my heater just has a high and low dial. It's really hard to get the temp to be completely consistent, and I feel like it gets a little colder at night. Is it better to maintain it at a higher temp or a lower temp? Should I try a better thermometer? Is there a trick to how to do this without making me paranoid and having to check and adjust the thermometer ALL the time?