What type of system do you have (reef, FOWLR, FO)?
Temp/salinity changes and feeding the fish (?) won't kill the cryptocaryon. Many have tried various psuedo cures for these pathogens, with various results, usually it subsides for a while only to return with a vengeance worse than before; the trophonts/protomonts grow in a cycle, dropping into the substrate and then re-emerging in higher numbers. This cycle confuses a lot of hobbyists, who think they have solved the problem, but the tale of woe is long for this industry-wide problem, and you need copper or starvation to be sure... that's right garlic lovers I said copper.
If you have marine ich in a fish only system and no quarantine tank, you can treat the main tank with copper just follow the directions and make a 20 percent water change in advance. It's better not to treat the main tank if possible, but if you have no q-tank it's better than watching your fish get eaten alive, and believe me, ich will kill every one of them. If you have live rock or other invertebrates it gets more tricky; the copper will kill the inverts, so you need to move ALL the fish to a quarantine system and treat them there for 30 days. Lowering the specific gravity (salinity) to 1.018 will help. This is the preferred method. While you are doing this, the trophonts in the display tank will starve. You can leave hermits, shrimp, stars etc. in the display, but you need a biofilter in the q-tank during treatment and monitor daily for ammonia. For some larger fish systems with large fish, moving them all may be impractical, so you will need to plan accordingly and decide whether QT or treating the main fish display is a better COA.
Also, be advised some species (i. e. eels, puffers, moorish idols, etc.) are harmed by copper treatments so research your charges.
