Since you've already medicated the main tank, I likely wouldn't bother with a hospital tank. At this point, you've already exposed the main tank to the medications, so will need to monitor it. If you can setup a q-tank for the angel, it would likely be better in the long run for the bacteria and other fish--I'd probably remove the angel to hospital, then do some large water changes and run some carbon on the main tank.
Raising the temp to 90 is pretty extreme, and likely will cause problems for the fish unless you are able to increase the surface agitation a great deal--warm water contains less oxygen than cooler water, and this reduction in O2 will not help the fish at all.