hyposalinity and side effects?

So my yellow tang suddenly got a bad case of ich.  He looked okay when I bought him at the fish store, and i quarantined him for a week (yes, i know, i should have QT for a longer period of time, but I always just follow a week and make sure they don't have an issue).  So anyway, I scooped him up and put him in a QT tank to start hyposalinity. 

But here's the thing.  In the main tank, he was covered in ich, but showed no side effects.  He was swimming around fine, wasn't flashing or scratching and was eating well.  He was hard to catch as he was just as active as always.  I set up the QT tank with water from the main tank (1.024) and dropped to to around 1.019 after he had been in it a little while (although not long).  Once in the QT tank, he hardly moves and barely swims around and acts like he is drunk or something and very lethargic, so now I am worried.  He was fine before going in the QT tank, and immediately following, he looks like he's on his last gasp.  The temp is the same (76) and the pH is fine, around 8.3.  No ammonia, nitrite, and about 10ppm nitrate. 

Is this normal? it doesn't seem like it.  he just kinda lazily floats around, and doesn't react to me when i touch the glass or even stick my hand in the water very close to him.  this i know isn't normal, so now i'm scared.  should i put him back in the main tank or just bare through it and hope for the best in the QT and hope he makes it through the night?

Thanks!

He's breathing relatively harder than normal.  I say relatively because i've seen him breathe hard like this when he didn't have ich all over him.  I have a maroon clown in the DT, but he's never had any spots or any symptoms.  He's as happy as can be.  I'm not sure about eating; I fed him yesterday before catching him.  I tried to give him a couple flakes last night when he wasn't looking so good, but he wouldn't eat that, so not sure.  I'll know if I feed him when i get home today if he doesn't eat, i'm in trouble, since he was just fine (other than being covered with ich) before i put him in the QT. 

He did make it through the night, and actually looked a little more perky this morning when i did a water change and lowered the salinity a little more. 

So new update.  First the good news. I went home for lunch and found that "Butters" as my fiancee calls him, was doing considerably better. He was swimming around and active and appeared happy, but still swarmed with spots and still breathing heavy.  I performed a small water change this morning and checked the salinity, which was around 1.017 or so, but I didn't check pH.  Last night when I checked it, it was right around 8.3. 

So for the bad news.  I made another small water change, and the salinity dropped to around 1.015.  I didn't check the pH immediately - I ate a sandwich in the meantime, but after eating I checked the pH.  It had dropped to around 7.35!  Odd since I didn't do that much of a water change and that pH would seem to indicate a lot lower than 1.015 salinity.  But, I use a refractometer, so unless I got a bad sample, that's what it was.  "Butters" seemed fine, was still swimming and alert, but the low pH startled me as I've read low pH in that range can kill the fish quick.  I immediately got some baking soda and peppered it in the water to raise the pH.  I ended up putting about two teaspoon fulls in it to raise the pH back to around 8.05 or so.  When I did this, "Butters" apparently went into shock and started to look paralyzed, all stretched out and not moving, falling over on his side and looking dead.  Almost exactly like what happens if you do a freshwater dip.  That made me panic, so I scooped him out of the QT and put him back in the DT as I didn't realize I was going to have this issue and hadn't planned to be gone this long during lunch.  I watched him for a few minutes in the DT before I had to leave to get back to work.  He seemed to slowly be recuperating and not acting like he had paralysis anymore.

I have no idea how he is now, but I'm shocked as to what happened...  what did happen???  Did I change the pH up too quickly?  Is baking soda bad?  Did I use too much baking soda too fast?  I've always used baking soda to raise pH in the past without any problem. UGH! 

Ah well, that explains it.  I'm not sure what planet I've been living on all these years - I've always just added baking soda slowly to the tank and let it go at that and never had any trouble.  until now that is.  My QT is 10 gallons.  I have a maroon clown and a couple green chromis. 

I'll just start over with new water and some buffer instead of baking soda which is what I had always used in the past. 

Thanks for the help!  If Butters is still alive, I will know better when I start over...

Start the hypo process over.  He's back in the DT at the moment since i had the issue with the baking soda in the QT.  He is doing okay in the DT... swimming around and active, but not eating.  Still breathing harder than normal, but the ich doesn't look as bad, which means i guess it's now all in the DT, but the DT was already contaminated.  Cleaned out the QT, will re-sead with water from the main and start over in a couple days after he has a chance to rest, assuming he doesn't get sicker from the ich, unless you think i should go ahead and put him in the QT and start over now.

Thanks!