I noticed, too, when I was getting rid of mine that they blow off pretty easily with a turkey baster.
Mucho Reef's freshwater dip routine is still the best first line of action, but it also helped to turkey baste the heck out of any zoos I left in the tank in between the fresh dips. I moved most zo's to a quarantine tank until they were clear and blew the rest off several times daily to keep the nudis from getting comfortable again. About the time they'd crawl their little selves back to the zo's, I'd blast them into the water flow again.
I don't know if it helped, but it sure made my day to see them get blown away.
Hah!
Good Luck! They're not easy to get rid of, but it is possible. I've been clear of them for awhile now.