Yes, if you read the article a little more closely you'll find your answers, but I'll go ahead and answer them for you here as well for the sake of completion in the thread.
1. Is it possible for an ich breakout to occur if you do not introduce new fish.
If yes, then where does the ich come from? (in my case I got it when I introduced new angle fish, but I am just curious)
Yes and no (w00t, I'm still king of the ambiguous answer! but read on, it's actually no) An Ich outbreak can occur in an established tank without adding new fish. But, this is really not a new outbreak. Ich has to have a lost to live it's entire lifecycle. Ich gets a reputation like it does because a lot of hobbyists fail to notice it where it most usually first occurs, which is in the gills which are easier to infest as they do not have a slime coat. If someone never noticed this (and let's be nice, gills are hard to examine) and had an infestation for a month or two before they saw it, they might conclude Ich is always present, which is of course false. So, the answer really is no, but it sure can seem like yes sometimes because you smiply have no outward signs of it existing.
2. Can ich live on a fish without you knowing it. Then after his immune system weakens will it come out?
See above. While it is true that some fish seem resistant to Ich (especially true of fish that have shrugged it off before) and that their immune system may come into play, usually once a fish has Ich, he has it until it is cured. It may very well be the Ich the lowers the fishes defenses in the first place which leads to further infestation rather than the immune system being compromised by something else. Let's face it, if you had a lot of little parasites in your lungs, you'd find it hard to breathe and your body would go into immuno-defense mode. Same with a fish. So, Ich targest weaker defended areas that affect a fishes overall health and may be the sole cause fo the immune system weakening.
3. How long after an outbreak is cured is it safe to introduce new fish. I lost my clown loach and can't wait to get another.
Okay, I am going to go all over the place on this topic. Ich is usually gone once you've treated for an entire week with salt and elevated heat a week after the last spot falls off of the last fish that has a spot. Having said that, I would be hesitant to add certain fish into a tank that still has the level of salinity a tank treated for Ich will still have for a while. This is especially true of scaleless fish like loaches. To me it makes more sense to have done several major water changes to reduce the salt's presence in the water. Also, I want to get on my soapbox now. If you've just treated for Ich, why on earth would you intriduce a new fish into that tank unless it had been through a regular quarantine? Not saying you would, but a lot of folks do and it makes no sense to me. Quarantine tanks are easy to set up and use and when used properly, they can literally save all of your tank occupants' lives. Some people complain about the cost or the space. Neither argument holds water (pun indeed intended). Q-tanks can be a ten gallon tank or a large rubbermaid container. You can use a cheap sponge filter or make one yourself easiyl enough. Needs a heater, some clay pots for hising places, and I like plastic plants because I can bleach them, though I know plenty of folks who use live ones and remove them if treatment calls for it. A q-tank only needs to be running when you have a new or sick fish. Otherwise, keep a sponge in your main tank's filter for it to remain seeded. I always have an extra sponge in my tank. After a qurantine and teratment you can just toss it and buy a new sponge. At any rate, a q-tank is affordable (I promise it is cheaper than replacing a dozen of most breeds of fish, which is what you can lose even in 29 gallon tanks that become diseased) can be stored away out of site when not in use and can save you money on dosing meds because it is cheaper to treat 10 gallons of water than 30 gallons any day. Anyway, I'm off my soapbox now. Just remember, if you had Ich, it came from your LFS because it wasn't in your empty tanks, it came in on stock, as you know, of course.
I hope that answers your questions and best of luck to you and your remaining fish. Also, if you don;t have a quarantine tank already, look into it.
EDIT: Gee, you people are faster than I was... of course, I got on my soapbox.
