Advice on HLLE

[i have crabs]

I have a yellow tang that got it about 8 years ago, happend after a large ich outbreak I did the low salinity thing and ended up having nitrates go through the roof from die off and that's when it started for me I cleaned up the water and started feeding selcon and other vitamin additives and it stopped but she is badly scared up and it never healed, she has the color back but the scaring got pretty bad,