Target reef temperature range
Most reef keepers target 78°F (25.5°C) as a stable setpoint within the acceptable 76–80°F (24–27°C) range. Coral reefs in the wild see 25–29°C; aquaria run on the cooler end to give margin for room temperature spikes.
Daily swing should stay within 1–2°F. Tanks that swing more than 4°F per day stress corals, especially SPS. The swing matters more than the exact setpoint — a tank cruising at a steady 79°F is healthier than one bouncing 75 to 82.
- Reef target: 76 to 80°F (24 to 27°C)
- Common setpoint: 78°F (25.5°C)
- Daily swing: under 2°F ideal, under 4°F acceptable
- Above 84°F: coral bleaching risk within days
- Below 72°F: livestock illness risk; some species die
Heater sizing
Rule of thumb: 3–5 watts per gallon depending on room temperature. A 100-gallon tank in a 68°F room needs about 400 watts to maintain 78°F. Split between two heaters of half-size each so failure of one does not kill the tank.
Always use a heater controller (Apex, HYDROS, Inkbird, Ranco) rather than relying on the heater's internal thermostat. The most common reef-tank emergency is a heater that sticks "on" and cooks the tank; an external controller catches this within a few degrees.
When you actually need a chiller
Most reef tanks do not need a chiller. Modern LED lighting puts out little heat, return pumps add some heat, and a moderate room temperature keeps tanks cool enough. If your tank stays under 82°F in summer with just a small fan, skip the chiller.
You need a chiller if: room temperature regularly exceeds 80°F, you run metal halide or high-power lighting, you have powerful return pumps, or your reef is in an attic / garage / room without AC. Chillers cost $300–$1500 depending on capacity.
How Reef Trak tracks temperature
Reef Trak imports temperature readings from Apex Fusion, HYDROS, and other controllers in real time, plus manual entry from any thermometer. Charts show daily swing clearly so you can confirm your heater is cycling properly and your chiller (if installed) is engaging when needed.