Help! Fish disease?

[Rondelet]

I agree, posting your water test results would be informative. Popeye and "holes" which may be ulcers, are usually caused by bacterial infections. Could be related to the temperature drop as this would stress the fish. But it may have also crashed your nitrifying bacteria, which may have caused an ammonia spike. This would definitely stress your fish, kill your starfish and cause signs related to ammonia burn (aka uclers and ratty fins) and popeye.

Without seeing your water parameters it's hard to say what is going on. I would keep up with the water changes and move affected fish to a quarantine tank. You could try a course of Maracyn-II at double the dose. If it was me, and if the fish were eating, I would go for an oral approach which is much more efficacious than topical treatments. You could try either Jungle's Anti-bacterial food - which uses a combination of several sulphonamides, or Seachem's Focus + any of Sulfathiazole/Kanaplex/Neoplex products, or Aquarium Products' Gel-Tek Ulta Cure BX.

Hope this helps.