give the tang a peaceful environment with green food materials as well as meaty foods and the HLLE may stop getting worse. Depending on how bad it was to begin with, it may even improve.
I have a Yello Scopas tang that i got with the latteral line's when i bought him,& it took about a month of good feedin,& they went away.Thats my favorite fish now all fat-n-happy.
No problem, good water condition, proper nutrition with vitamins added. And he will be fine... My little pt has been improving since I got him. My large pt has totally recovered. Both had it when they came to me.
you can soak food in marine vitamin c,(Kent makes Marine C and Marine Zoe which are good) as well as fresh Gracilaria algae which is very good,i'm sure someone on the board has some growing they wouldnt mind giving you.
Its not a lost cause by any means. I cured my yellow tang of HLL using a combination of the above treatments and he is still going strong. Also make sure there is no stray voltage in the tank as this could be the cause as well as poor nutrition.