Naso tang not doing so good

[Jefftopgun]

So I stepped up from a 9 month old 76g setup to my current 250 (8'x3'16.5 inch WL). I had an YT (4 inches) and an falco basslet (4 inches) in there as they had chased out all my livestock (poor skunk clowns and a lawnmower). I finally broke down and picked up some more fish (I've been more of a coral guy for a long time). I got a naso, regal, and sailfin tang(all 2-3 inches) and, oh yea more coral around black Friday. That said the fish have been in my tank for about 3 weeks, all have done well, eating just about anything I put in tank (cheap flakes, nori, pellets ect.). Last week, and this was probably a dumb decision, I stopped by LFS and they had a gorgeous Niger trigger ( roughly 4.5-5 inches for 60$) and he got me lol. I wanted a blue jaw bit took the chance on the Niger and he has been a model citizen, and is my new favorite fish, I cant tell you the last time I actually sat in front of my tank just to watch fish (I do for my coral all the time).
Now all this being said, since the introduction of the Niger, the naso has seemed very reclusive. Even when he is out and I feed the entire tank, and everyone is going crazy, he just aimlessly floats, a bite here and there. Today hes only left his rockwork hiding place twice. Breathing seems normal. No white specs but he does have some whitish banding that comes and goes (as I've been told nasos, especially juveniles, do). No head twitching. Water parameters are app good, sans a slightly higher than desirable phosphate (.15ppm I blame this on all my extra feedings trying to give him a chance).

So to the meat and potatoes. I have a spare 20gal, heater, a few pumps/powerheads, should I risk the stress to snatch him up and throw him in there so I can give him less competition for food and stress. I'm already worried even though I've only noticed these symptoms for 3-4 days, (and have seen him eat, but only a few mouth size bites of nori) just didnt know how long was too long to wait, or if maybe this is q naso thing and he will remain elusive until he grows into the king of the tank

 

[Jefftopgun]

Well hes in a 20 long with a 200gph pump for circulation/surface agitation and a heater, stole a pair of small rocks from my sump and threw a little bit of nori, some random flakes, and a few pellets in there with him, thought I might have caught him eating at one point, he pooped when I netted him so at least he had something in his system, planning on running a pair of nearly matched pumps 3 times a day to cycle his water back to main system due to lack of established filter system. Have enough salt on hand for 2 100 percent water changes so if anyone can give me some recommendations for a dosing regime by chance I can actually treat it as a QT versus having him in a low stress environment (ie sumped as he basically is since the 20 long is next to my sump under tank). Something to be said about having 24 square feet of play room under the tank.

Hes still very lethargic, not eating much if any. Respiration does not seem labored or quick, no head jerking/twitching/or itching. Hes lost almost all his color and is nearly black with large white spots/streaks (can be seen if you just Google naso tang white spots), entirely too large for ich/velvet. Got a good look at him and didnt see any flukes but am open to freshwater dip. His poop seemed relatively normal, not solid round stool like my YT normally passes but not white and stringy or anything. Does not seem to fit symptoms of HLLE although I guess this is possible.
I feel like I'm watching him die I need help guys.

 

[ca1ore]

White blotches on N. literatus (I assume that’s what it is) is normal. I have had very little luck with small Naso tangs; they don’t seem to acclimate well and are often poor eaters. Just try to keep stress to a minimum and offer as broad a variety of foods as you can.

 

[Jefftopgun]

Sadly he didnt make I through the night. I did a quick inspection on the carcuas, no ick, no flukes (although I've heard they drop within hours from a host due to lack of blood supply). So I now have a QT tank under my DT, with the ability to hold livestock.

So myquestion, I snagged 2 rocks out of of my sump to act as a bio filter for the qt. One of which is covered in gsp (and I know it grows like a weed, but I'd hate to just chunk it, but given that the fish was only in my qt for about 14 hours, and came from my display), is there any chance that I would be introducing anything that wasn't already there by putting rock back in sunp.