Good stuff Walt! To add to that, I was at a talk by Ron Shimek, an invertebrate zoologist well known in our hobby, who said that actually the healthiest reefs with the most life are actually pretty warm- usually at about 82 degrees. When our tanks are cooler the corals' metabolism slows down significantly so that they are actually almost starving. The only problem with having the water warmer at 82 is that their metabolism are much higher and without proper care and feeding the corals' health can go south pretty quickly. Shimek also said that temperatures frequently vary just like Walt says, and that its actually un-natural for us to keep our tanks at a set temperature all the time.