I agree with rogger... I don't like a temp swing either. That being said, not one of my tanks has a temp swing lower than 4 degrees. Lights off on the 65g, 78 degrees. Lights on 5 hrs, 82 degrees. Lights off 18g, 76 degrees. Lights on, 81 degrees. Nano lights off, 77 degrees. Lights on, 81. Every one of my tanks would be considered successful. I get lots of complements on my tanks. I think that even a temp swing is okay to an extent as long as it's reliable.
I've heard lots of people say that it's not the conditions, it's the stability of the conditions. I hold true to that quite a bit. Things mainly go wrong when they change rapidly (hence the popular train of thought, bigger is better, since changes happen more slowly.) I recently went to a friend's house who was having problem with xenia. She had lots of other corals flourishing. Only xenia was the problem (actually, she had just lost a favia, but it was fairly new and maybe unrelated.) I tested everything. I then broke out my test kit and tested again. Her phospate kit wasn't working, and phosphates were high. A little digging revealed that she does about a 5% water change every month. Phosphates rose slowly over time, until they were starting to affect a few corals. If my phosphates were half what she had, my corals start stressing bigtime! But hers accumulated slowly, and they got used to it. (Weird thing was, no algae. Anywhere!) I also know someone who keeps his reef tank stable at 84 degrees. Beautiful corals! Reef's Edge keeps their corals gorgeous at around 76 to 77. How's that for a temperature swing! Alot of the same corals in both systems. Corals are a lot hardier than scientists want you to believe. Given proper care and close scrutiny, they'll survive just fine.
