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Water Chemistry

Reef Tank Temperature: Stability, Chillers, and the 78F Sweet Spot

Why 78°F is the reef target, when you need a chiller, and how to use room AC strategically to avoid one.

By Saltwater Aquarium Guide Published May 10, 2026

Blue-and-yellow spotted wrasse swimming over a green brain coral — Photo: David Clode / Unsplash

Reef stability matters more than the exact target. Most experienced reefers run 77–79°F with daily variance under 1°F.

When you need a chiller

If your tank exceeds 82°F in summer or your room AC cuts out at night, a chiller becomes mandatory. Powerheads and pumps add 1–3°F of waste heat.

Cheap alternatives

Lid off + cooling fan blowing across the surface drops temperature 2–4°F via evaporation. Just upsize your ATO reservoir.