[DrHank]

I'd recommend that you end this hypo treatment and get him back to normal salinity and ph fairly quickly. I'd be doing 50% water changes (probably twice daily) until both salinity and ph are back to normal.

At the risk of sounding stupid, may I ask why you were performing this hypo salinity procedure? Some marine fish do acclimate to brackish or even fresh water however, the Naso tang spends most of it's life on the outer edges of the reef. It isn't one that will.