For a bit of history I'm a 20 year freshwater tank user that just switched over to salt about 6 months ago. I'm trying to do it 'right' by placing all new aquisitions into a hyposaline QT for a month prior to moving them in. The first group a blue tang and maroon clown did fine, but my next group of fish didn't do so well.
The second group was some green chromis and a sailfin tang. They were doing alright until about the 3rd week and it looked like they started getting some fin rot because the fins were looking tattered without and apparent fin nipping by any of the inhabitants. So I hit the tank with Melafix and things seemed to be getting better. I took out the carbon from my filter in the meantime, and the water was getting cloudy. Near the end of the treatment, most of the fish started getting white fluffy spots on various parts of their bodies/fins, even though the fin rot seemed to be getting better. I did a water change and started in with Pimafix for presumptive fungal infection. Still no carbon, so the water was getting cloudier and cloudier, but still tested fine. After a few days of treatment that again seemed to be helping, the fish all seemed to be distressed breathing heavily, and the next morning they were all dead.
Now, I'm on my next 'batch' with a flame hawkfish and an orange finned tang, again right at the 3 week mark. Now the orange tang is showing tattered fins and cottony white spots on the body and fins (just a few). This time I decided to go right for Pimafix, but this time leaving the carbon in. Its been 3 days, and now the fish are starting to breath heavy. I'm going about 50 water change tonight in hopes to save them.
Any suggestions? I'm just trying to stock my 115 gallon aquarium that looks pretty pathetic with just a blue tang and maroon clown, but I can't seem to get my fish to survive quarantine.
Parameters are as follows:
Ammonia and nitrate: 0
pH: a little low at 7.6 (just added some buffer to increase it)
Hardness: don't remember the number but it is fine.
I typically do a 20% water change weekly and have a sponge filter and a corner filter with carbon in it. I have a piece of live rock from my main tank in the QT also for additional bio filtration.