I have 18.5 year old orange tang and a YTBlue tang that each have significant hlle
In the same tank is a purple tang that is in between in age...no hlle
There has never been any carbon used in the system
The fish are well fed
The cause....debatable
In general, I’m sure it’s a handling and husbandry issue along the way.
And I’m sure many hours in a small bag with minimal water that was probably “dirty” prior to shipping doesn’t help
Probably best to leave them on the reef
Oldest 2 stars I know of
Green brittle star (the huge scary kind) that is well over 10 years
Sand sifting star in a 200 deep sand bed, over 8 years
Good luck, positive vibrations