Sometimes, cooler water in our aquariums can be just as dangerous as warm water. Corals in captivity can survive in a temperature range of several degrees, but thrive when that fluctuation is very minimal. Hard corals typically do best from 78-82 degrees, at least in my experience, and start to show slower growth rates outside this “sweet spot”. When temperatures get too hot, the corals respond very quickly and often bleach out. Fortunately, the cool water’s effects don’t act quite as fast, though they can be just as severe as warmer temperatures if allowed to persist long term.