How do I know if I need a chiller?
If your water temperature exceeds 83 degrees and fluctuates more than two degrees during an entire day, you may need a chiller. You can also try heaters and cooling fans. With heaters, you'll have to keep your temp at the high end. With cooling fans, water will evaporate quickly which will require frequent top-offs. Top-off means adding freshwater due to evaporation.
Temp Should Not Move More Than Two Degrees:
Keeping the water temperature constant is important for any aquarium. The temperature should not change by more than 2 degrees within any 24-hour period. Faster changes in temperature can cause fish to become sick, especially through outbreaks of ich.