Hi Jim
I got the Purple from an online store, before he sold it to me he told me he had HLLE, so I got a cheap price on him. I figure it was just the stress from being caught and handled. I have an established tank, it's just over 4yrs old, with a 2" sand bed, give or take. No ideas what my phosphates or nitrates are, don't bother testing for that, although looking into phosphates, to see if it has any effect on my acros, but that's another subject. I use Tropic Marin salt, and only do a 30g water change every 4-6months, on my 180. I did soak all my frozen food, mostly mysis, in Kent Zoe, and Kent garlic. Also feed flake foods, which already had garlic additives added to it. Other then that I don't dose anything else to my tank. There are 2 other tangs in the tank, a mimic, and yellow. The yellow, and purple fought good for a day or 2 then that was it, the yellow taking the worst, and being a tad bit smaller. But now they are great. all my fish get along, and have no stresses. I think with a good mature/healthy tank, and good nutrition, stress free environment, this is a cureable disease.