Cool, thanks for the info. I like the walling off idea, although it'll be somewhat of a last resort just because it'd be nice to not do the work if I don't need to.

My main tank (reef) would be downstairs, and I was debating whether to make this reef or FOWLR. I could make it FOWLR and use fake corals, similar to the Helotes El Chaparral tank. I think my last remaining question is, how effective are chillers? Do they work well enough that the water temperature will be fine, and it's just the room heat that's an issue? If I can't control the water temp all bets are off, but if I can do that then I'm sure I can swing something to make the attic bearable. The fish are my main concern, attics are meant to be hot.

Sorry if I'm sounding like one of those people who asks for advice, gets told that it's not a good idea, and proceeds to say "screw you, I'm doing it anyway." I'm just tryin' to find a way.