I've had a small bout of black ich with my YT, but the clowns and chromis never picked any of it up.
I think the chromis are less susceptible, as they have a harder layer of scales, unlike clowns, which are like tangs, and have softer skin.
(Somebody correct me if I'm wrong here).
180G build thread
180G All-glass with dual megaflows in a custom stand
AquaC EV-180 skimmer
250 pounds LR
160 pounds aragonite
Custom acrylic sump from GlassCages.com
2xPCX-40 return pumps
2x250MH 14K, 2x175MH 14K - PFO lighting, 2x65W PC
No-name 36W UV
Water General 125GPH RO/DI