very confused!!!loosing fish

I'm going start back 3 months ago. I had a great 30 gal, me and my brother-in-law traded some live rock and I started getting algae so my wife and I took the rocks out and scrubbed them and did a 50% water change, tank was going great. So we went and bought a mating pair of clowns, anemones and cleaner shrimp. One week later my male clown wouldn't move his mouth and died then my female clown does the rapid breathing thing and also died. I checked water and everything was fine so I assumed I bought sick fish. I laid off the fish for a couple months and dealt with the anemones and shrimp,then I started getting a lavender almost black film on rocks and and some stringy moss stuff, went to the local fish store and he said that was great stuff my rocks were good and I can get a tang to eat the moss, so I wanted one and decided to get it and a yellow striped maroon clown, check all perimeters and everything looked good, tang didn't last 24 hours. Laid on the bottom with rapid breathing and died, the clown is ok so far and my anemones and shrimp I had for months are also doing great, I'm at the point where I don't know if I have a disease in my water? Do I tear the tank down and start from scratch?How do I figure this out? Nitrites and nitrates are low, ph is 8.3 salinity is 1.22. Don't know whats happening. Please help, maybe its this algae stuff?
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How low is low on Nitrites/Nitrates?....did you mean to type 1.022 for sg? if not that may be your issue? also if you have excessive algae taking up all the oxygen in the water that may be contributing as well?

 

lol yea i meant 1.022,,i kinda thought the same thing but i have a 12inch air stone inside,,would that make up for the loss?

 

also ihave an orange tree sponge thats doing good

 

but i dont like the lavender algea

 

nitrites dont even register and nitrates is 1.0

 

It sounds like low oxygen?? If you have an airstone, that would seem to help so that doesn't make sense but the description of the fish does....hmm....have you been running anything new on the tank? added any reactors? additives? can you agitate the top of the water with a powerhead? What do the fish look like besides the heavy breathing? do they look grayish in coloring?

 

How did you acclimate your new fish? And also, the LFS should know better than to sell a Tang to someone with a 30 gal tank :/

 

I have added buffer with calcium, my power head is about center of the tank. Color doesn't change, its always sudden.

Would the tang have died because the tank is to small? Was he too stressed?

 

I would suspect the tang died do to stress. It happens, they are very sensitive. Small tank and low SG might be the cause.
It sounds like you had an issue in your tank. Having an anemone, shrimp and coral OK would either lead to a disease or low O2.
I would increase your SG to 1.024 ~ 1.026 your Low SG is not enough to kill a fish but could have contributed to the difficulty acclimating a new fish

J