Fin rot is very often caused by flexibacter.. the same critter that manifests as columnaris, so it's a sort mild/early version of that disease.
Columnaris can exist in cold water (goldfish get it too) but it really likes high temperatures, 76 and above, and it moves pretty fast in a tropical tank. So raising the temp on a fish with fin rot/skin or fin fuzzies/breathing issues/septicemia/open sores and other symptoms of that bacteria isn't always a great idea. Fin rot can be caused by other things as well, but as columnaris can be very fast moving indeed (I lost a fish to the slow version..), I personally don't like to take chances.
Higher heat works with ich, because the ich parasite hates heat above 83 or so, but it can make a columnaris infection speed up. 78 is an acceptable heat for bettas, so I try to keep my hospital tank at around that for anything that looks like a bacterial problem, just to be safe. That's just how I do things, I'm not saying it's THE thing to do. But slightly lower temps seem a good idea to me, when a common cause of it flourishes in 76 F and above.
Last edited by Aus; 06-19-2012 at 07:53 AM.