"pimples" on fish are opening signs of encysted worms or microsporideans. Quarantine and treat with a medication for protozoans, something like rid
ICH+ should do the trick. Other typical outward signs of this problem would be lethargy and general lack of appetite. If it does not exhibit lethargy and lack of appetite I would stake out the tank like suggested in the next paragraph.
It is also possible that your fish may have gotten stung by a coral or another fish and it is a sign of irritation. Before treating in a quarantine tank I would highly suggest taking a day and night this weekend to watch the tank and look for signs of aggression from other fish or possibly stinging from corals. If it does not go away after a few days, then quarantine the fish and treat for protozoans only if you are sure there is not something else in the tank causing it first.
Sometimes cleaners can get it off if you have any neon gobies/cleaner shrimp.