Update:
The lawnmower blenny (in my brother in-law's tank), the two clownfish, and the blue tang are doing extremely well. I believe the tang had a mild case of lymphocystis which has completely disappeared after treating with Maracyn II as directed by LA to do so. I'm not sure if the Maracyn or the decrease in stress / increase in nutrition is what made it go away but it did.
I am going to treat the tang for ich with hyposalinity. I have noticed a few subtle white spots on the fish's body but never more than one or two at a time. It's fairly difficult to tell whether or not it is actually ich when it isn't showing a severe outbreak.
This treatment is safe and won't cause any harm to the fish if performed properly, correct? I'd just hate to have this fish in QT for 4+ weeks and then add him/her to the DT only to find out that (s)he actually did have a mild case of ich.