What I hear you saying is that you believe your ich problem to be a result of a previously infected fish that seems to be giving it to your other fish and because no one can tell you for certain it didn't happen that way you are going to run with it. And, to top it off, you'll keep asking around until you find someone that agrees with you and will give you advice you want to hear to "fix" your problem.
By putting all those fish in your system you have stressed them to the point that their immune system is compromised. If the tang was infected before you got it (doubt it but let's say hypothetically) then your other fish would be able to "shake it off" if they were in a good environment. The flu kills those who have compromised immune systems. If you try to push the limits without knowing what you're doing, your going to crash your system, be out a ton of money and worse, kill fish and corals in the process. That tang would have made it if it were QT'd then put into a healthy tank that was big enough for it to move properly. Your ignorance and desire to go too fast is a deadly combination. You said it "Unfortunately I do not have a QT tank ready. I am actually using this tank to hold a couple fish for my friend. I get the fish practically free through him at wholesale ($8) so it is actually cheaper to not treat it. If it was more expensive then I would have for sure." If you've been in freshwater forever, you're telling me you don't have a little tank you could have used to QT these fish or to treat them if necessary? You have some extremely intelligent people, people who are college trained, people that work in LFS's and professional aquariums, these people are all telling you that they have seen people switch from fresh to salt and not let go of their freshwater paradigm to the detriment of their tanks. Why do you think you are different? What makes you special?
I really wish I could "agree to disagree" in this but I worry about the fish and corals you are going to kill. PLEASE, fix your tanks, set up a QT and do it properly or get out of saltwater. There are many ways to do something but there are a lot of idiots out there that will tell you what you want to hear just to kiss butt or to make a sale. Do your research and follow the rules. Learn why the rules are there before you try to bend them. Please, don't let your ignorance kill more fish.
C