These fans good or bad?

[Delphinus]

Sure, you don't need a 12 VDC power supply for the AC ones. Just some wire and a plug and you're set.

Over one tank I have DC fans (Icecaps). Over the other tank I have AC fans. The AC fans are Orion's, and are in fact, quieter than the DC fans. Other than that I don't really see any difference. The only thing I can think of, the DC fans can be regulated so that they have different speed settings. I.e., if you apply 9V to a 12V fan it will run 3/4 as fast. Useful if you want a variable speed (i.e., bump up the setting on a particularly hot day). I think you can do the same thing with an AC fan if you use a rheostat (but don't quote me on that as I have no idea what that actually means. I think a rheostat is something that looks like a light dimmer switch ... but I don't know if it's more complicated or not.)