Greetings. Im sorry to say but your tank sounds like a recipe for disaster. I will try to suggest the right things. Not a personal attack at all.
First off there are way to many things in that 45. Two tangs, which really shouldnt be together beacuse of interspecies fighting, each of wich will out-grow the 45 even if they were alone. Tangs need huge tanks with lot of swimming room. I hope you take them back. The second thing and maybe the most important is to research the ich parasite and ts lifecycle. Its been talked about so many times and the info is so available I cant tell you here. QUARANTINE ALL NEW FISH FOR 4 WEEKS MINIMUM to avoid parasite infestation.
My suggestion is to learn about hyposalinity. Get a refractometer, pick up a hospital tank (like a 30 or 40gal) and put ALL your fish in there for at least 4 weeks with 6 weeks even better. This will eradicate the parasite from your fish and your display tank(which will have to remain fish-less for the whole 4 to 6 weeks). If you do this, please be careful to maintain the highest water quality possible in the hospital tank. You will be doing lots of water changes in the hospital tank to keep the ammonia down, as this is a often overlooked thing, and most likely a large reason for fish death in hospital tanks, as opposed to the actual parasite killing the fish.
This is the only way I see you getting out of this with the least amount of losses.
Youve already spent a ton of money on your tank and fish. Dont skimp now or it will all be wasted.
Good Luck and keep asking questions.
John
