Saltwater Angelfish Need Help!

[Shauna44]

I have a small Coreal Beauty Angelfish and a yellow tail damsel in my saltwater tank. The damsel is fine. Today I noticed the angelfish was swimming erratically and fighting to get to the surface for air. I checked all of my chemical levels and the are fine. The water is clear and my tempature is good. About an hour later my angelfish is barely swimming, but trying very hard. He is also laying upside down or on his side. But he is still alive. The levels are still good.
What is wrong with my fish? He has the symptoms of a bladder infection, but I am no expert on sick fish. Is there medicine to cure whatever is wrong with him? How long will he last without medication?

 

[FroggyFox]

when you say the levels are good....can you list them here? ph, SG, temperature, how long has the tank been set up, nitrates, how long has this fish been in the tank...

Sometimes when you think something is fine or you didn't think to test something, one of us might be able to help.

 

[Shauna44]

My fish was dead when I woke up this morning, but I still want to know why.

20 gal tank

ph at 8.3
ammonia, nitrate and chlorine 0
salinity 1.022

The only other fish i have is a yellow tail damsel. I've had him and the tank for about three week
I found out today the pet store I bought the fish at uses chemicals to catch their fish.