is my tank dieing?

[reef_friendly]

i got a powder blue tang 2 weeks back. it was absolutely healthy with no signs of white spots. i introduced it in my tank after 2 days and it started turning white the same night. i found it dead the next morning. now my fish r behaving in an unusual manner. the tangs r not running after pellets as they used to do. lost a damsel, and the other one has developed dark blue patches and white spots, my unicorn tang has a swollen eye, sailfin has a few white spots.
the yellow tang and fox face seems healthy. my worry started when i didn't see my fish roaming around in the tank. they all were hiding in the rocks. what should i do? help!!!!!!!!1
i'll be doing a water change tomorrow and have increased the temperature by 2 degrees

[supertech3]

what are your water parameters? the powder blues are very prone to get ich

[Gundo5000]

I'd do multiple water changes over the next couple weeks.

[Tokey]

I had the exact same thing happen to me. I added a hippo tang and a coral beauty. next thing I know the hippo had white patches and every thing thats happening to you happened to me I did daily water changes as I was losing a fish every day or 2. I also added garlic to the food but eventually every fish stopped eating, I now have a tank with no fish just one shrimp and some snails. I hope you have better luck than I did. Some of those fish were 4 yrs old it really hurt to lose them.:(

[reef_friendly]

water parameters r fine. my temperature was a a bit low that i have corrected now.

[waterfaller1]

You should not be adding tangs to an established tank without quarantining them...asking for trouble. {or most fish for that matter}If you want to help the fish you have...read here:
http://www.petsforum.com/personal/trevor-jones/hyposalinity.html