frustrated! fish dead

[asherah]

So it seems my tank is doomed to only have 2 fish. My diamond goby and my clown. Seems everytime I add a new fish they die.
I bought a small blue yellow tailed damsel last week and he was doing fine.
I saw him eat. Then 2 days ago he started hiding and this mornig he is dead.
I dont understand it.
That's what happend to my other fish I've added aswell. So strange. =(

Ill do some tests on my water and post them later but my goby and clownfish are happy. =/

The tank is 1 1/2 old now and the salinity is o.o25. I dont have any crabs, I feed the fish once a day at night. they get fed some marine flake. Sometimes I put some shrimp in the tank for them.
I have a skimmer and koralia 2 in the tank for flow. There's no algae in the tank either.

Any ideas ?
asherah