Parasitic Tank?

Question
I have a 20 gallon saltwater tank with a chocolate chip starfish, and a sixline wrasse. I had a cardinal fish and a blue-green chromis. Yesterday morning when I woke up the chromis was swimming vertically, fighting to stay afloat. He seemed to be gasping for air. I scooped him up in a net and propped it so he was contained, but still in the water. He was panting, like a dog would. I thought he was hurt, or might have had swim bladder. I checked all nitrate, nitrite, ammonia, and PH levels, all was good. I checked the salinity and it was @ 1.022. the Chromis died shortly after. The cardinal fish(I lost him a few weeks ago) Had appeared to be gasping for air as well and died 2 days after I put him in the tank.

My tank was a hand-me-down from a friend. it has crushed coral at the bottom. when she moved it to my house, she left about 8" of the original water in the bottom. She was never able to keep any fish alive in the tank. So I then thought the tank may have a parasite of some kind.. How do you know? I have been told to remove the live rock and lower the salinity to kill the parasite; and i have been told to strip the tank, bleach it, clean it; throwing away the original substrate and starting fresh. the second suggestion makes more sense, but what about the wrasse and the CC starfish? if they have the parasite as well, wouldnt that contaminate the tank again? how do I know what to do??? I dont want to kill anymore fish!!! Help me!!!  

Answer
STARTING OVER IS PROBABLY THE BEST SUGGESTION. BRING YOUR CREATURES TO YOUR LOCAL FISH PLACE AND GIVE THEM UP SO THEY SURVIVE. MY PLACE WOULD EVEN HOLD FISH FOR ME BECAUSE I BOUGHT FISH FROM THEM. SOMETIMES FISH DIE BECAUSE OF THE WAY THEY WERE HANDLED IN TRANSIT. MAKE SURE YOU ACCLIMATE NEW ARRIVALS BEFORE YOU PUT THEM IN THE TANK.