I could live with it as long as the fish are comfortable. I travel a lot and can't take chances of fish dying when I'm away.
I think you misunderstood me, I didn't mean live with it in that the fish would be comfortable, I mean live with it in knowing that you can and probably will lose fish to disease due to you not being able to deal with a second tank to treat/watch incoming animals. Basically again telling you that there is no magic bullet to treat diseases in a full coral reef tank.
These diseases are so unpredictable to know when to stop. Cos stopping with what I have doesn't mean diseases won't get in anymore.
But they're not unpredictable, you either have them in your system or you don't. If you have them, they can pop up if fish get stressed and immune systems get compromised. If you don't have them, you won't get them if you don't put any new stuff in tank. If you have a tank running for a months with no signs of disease you may be in the clear. If you want a fish and don't want to QT the fish then that clock starts back at zero as far as how long it's been as to whether or not you have diseases. You mentioned the last fish you had was 3 weeks ago. That's well within the life cycle of some common parasites, so it could have come from that, it could have also have already been in your system and something just stressed out the fish (and now it got compromised).
Thats the other problem... QTing fish is one thing, but if cysts could get in via coral or other inverts, its crazy to have a mirror system (with the right light, params, etc) to QT coral!
Not really that crazy, ignore fish, well there are some nasty coral parasites out there too, and some people have frag tanks as well. And you don't have to have a mirror system, just a system that can keep things alive for a period of time. Fish system, doesn't need to have as high a specific gravity, coral system, just get water moving around with some minor lights they'll survive. Of course another school of thought is forget it and simply go with coral dips hoping that kills any buggies (I'm not sure if it will kill ich cysts and what not), and put them in your tank.
Now I'm starting to think a nano tank with 2 fish and lots of coral might have been a better fit for me. Contrary to the norms of reef keepers upgrading to larger tanks
Well you have to realize the "norm" of upgrading to larger tanks means EVERYTHING needs to upgrade. If you had a nano and went to a 120g tank you are not going to get away with 2 gallon water changes every week, so you have to change what you do if you expect similar results. If you put every fish in that you want at the beginning and nothing shows signs of disease after a couple months I think you're in the clear to just sit back and relax, but if you want to put in one fish one month, another fish 3 months down the road, well you're risking all the other fish in your tank unless you quarantine incoming fish, if you had a nano with 2 fish... not as big of a deal, if both fish die then you lost 2 fish, wait a period to let whatever kill them die off in your tank, and start over.
Look, I know it might seem like people are ragging on you for what you're expecting, but we're not. We're all reefers and most of us probably have had similar issues at one time or another, and were simply trying to point you in directions that are known to work.
FYI, I was told CP does break down in sunlight, so it's not like copper where it stays infused into your tank for all eternity.