Hyposalinity method: how fast should I lower salinity?
 

I bit of a background: I have 5 fish in my 30Gl quarantine, two small blue tangs, a fire fish, 6-line wrasse and a goby. They have been in the quarantine for 4 days and tangs developed Ich, so I am now looking at different treatment methods. The good thing is that this is dedicated QT and they can be there for as long as I need them to be. I have found excellent article by Steve on reefkeeping.com and it appears that hyposalinity method should be optimal for me. I intend to keep all fish together since I can't rule out that others are not infected even though only Tangs show the signs at this time. I removed the sand and piece of coral that were there and put more PVC plumbing parts for hiding. I also raised temperature to 80F. I plan on wiping the bottom and PVC parts regularly since it is now all just bare glass and plastic.

However I have a question: how quick should I lower salinity at the beginning? I plan on slowly replacing salt water with RO/DI fresh water in the whole tank. I suppose doing it too quickly will cause stress and doing it too slowly means I may miss the moment Ich starts falling off the skin of the fish.

Thank you!
Vadim