Disease help

[fishoholic]

So something is up with my tank that doesn't make much sense. I'll start with the symptoms my fish have.

The main symptoms are: some fish have very pronounced white ich spots (looks like spec's of salt on them) some fish have colour loss, some are breathing heavy, some have fine white spots on them like they've been dusted in flour (although one thing I do know, is that whatever they have it isn't velvet, as I remember very well what that looks like) some have cloudy eyes, some are not eating and others are just fine like nothing is wrong.

It's been mostly going on for a week now but some of the fish had bad ich on them for awhile, and my regal tang was the first to die about a month ago, which at the time I thought it was just from bad ich and stress that maybe my Sohal was causing.

Ammonia 0
No2 0
No3 20-25

My phosphate is really high and I hadn't run carbon for the last month because I kept forgetting to replace it. Last Thrus. I moved all the corals out of the tank and since at that time I had only lost a few fish (and the remaining fish didn't have much external signs of disease) Steve (who used to run Little Oceans) and I thought maybe it was some sort of internal parasite so I started treatment with Kanaplex. I've done 2 treatments and while my pink tail trigger went from not eating to eating the other fish started looking worse and a couple more are MIA and one found dead. So tonight I plugged the skimmer back in and started running a fresh bag of carbon.

The plan for tomorrow is to catch all the fish and put them in QT. The problem is I don't have a clue what to treat them for. Part of me is thinking FW dip then slowly do hypo salinity and part of me is thinking formalin, although I've heard formalin is tricky stuff to deal with which makes me a bit leery to try it.

Any ideas? thoughts?