Acceptable Temperature Swing?

[sphelps]

Depends on the corals you keep, some are more sensitive than others. The more steady you can keep it the better. Maintaining you tank temp a little higher @ 80F will typically result in less swing than if maintained at 78F.

If it jumps up 4 degrees once in a while on those hot summer days I don't think it's a big deal but other than that I would aim for less than 2 degrees.