Any chance you have any pics. We should have asked for that immediately. HLLE usually makes the lateral line look whitewash. If it appeared to be "popping out" maybe it was emaciated. Like Bang said they need the algae, that is what they've evolved to eat so if it isn't getting enough algae, even though it is eating tons of meaty food, it could still be malnourished and die. I have never dealt with HLLEpersonally so I may be very wrong. I don't think it is a fast killer. There is a very sad looking 6" naso at the only fish store near me in a 20 gallon tank with a severe case of HLLE. His whole lateral line and head is eroded. It's been in the tank there for at least a year, gradually getting worse. Obviously I never buy anything there unless it is an emergency.
I like to buy the Rods algae sheets. They have a variety pack.