Sick Fish...HELP! (Newbie)

[63valiantragtop]

Hi there...

I have a 90Gal set-up with love rock, 30gal sump, overflow,skimmer...

I bought the tank 2nd hand (about 3 months ago) and it was already running but with a fluval 404 filter. I saved about 80% of the water at the time I moved and reset it.

I wanted to change to the sump/skimmer.

The tank already came with one large (about 10'') Naso Tang and one small oscillarus clown. I added a few small angels, a toby puffer and a butterfly.

I had a nightmare of a time getting it all reset-up, but it is now done.

Now that I finally got everything running my fish are sick...and dying.

I have lost one small bi-color angel and the Threadfin Butterfly. My puffer is discolored and hanging by a thread. My big Naso Tang has spots all over him (but not white and "ich" like)...more like lil' black marks and his eyes are a lil' cloudy and he seems to be "resting" on the bottom alot, which he has never done before.

They still eat well at feeding time.

I was told by a guy at Big Al's to use this "no sick fish" medication. It is the size of an eye dropper and cost me $80! I have been using this for 3 days and see either no improvement or if anything it is worse...

Can anyone give me any suggestions?? I am new to saltwater and I am dires straits here....

I can post pix or water quality reports if that would help.

Thanks alot.

Jason.