My Powder Blue Tang has not eaten since I purchased it 12 days ago. I have tried lots of different foods with no success. Over recent days the Tang has developed a small cluster of bumps behind the eyes. I suspect this is a parasite infection. The LFS told me to place the fish in a tub of RO water (with no salt) at correct temperature for three minutes then return the fish to the tank. This needs to be repeated for three days. Is this sound advice? Can you please advise me what to do. I would like to return the fish to the LFS but I don't think they will accept it back in this condition. I fear that I am running out of time.