Hi Paul,
I agree that the established tank is the key to success.
I keep putting off setting up a nice big tank because I end up moving around, and I don't want to get into getting the tank established and then destroying everything in it by moving.
I read post after post of people setting up tanks, and from the point they first mix the first batch of saltwater to when they are adding fish is days or weeks... and then they are all over with "Help! my xxxx fish keep dying"
What do they do? They keep going with knee jerk reactions and miracle cures and adding new fish, and never letting the system get stabilized and established. Many don't do any quarantine period, or only quarantine fish but are always adding frags from a friends tank or a new coral from the LFS without thought that these are also vectors for introducing bad things to their tank.
My last post was more to get the attention of others reading this thread than you. A lot of people out there read things so literally and then they are off to the LFS and are going to do something that one person said worked for them without understanding why. I read a post a few weeks back about a person who was literally cooking his live rock... i.e. boiling it, after having read some of the threads about live rock "cooking" to clear out phosphates and other organics by bacteria.
I can only imagine somebody reading this thread and thinking "wow, thats a great idea... I'll introduce Ich to my tank on purpose to help my fish build up an immunity" as if it is like a vaccination so they don't have to worry about introducing new fish and having to go through the "hassle" of quarantine.
I read a lot of articles about ich and its treatments a while back, and I really wish I could find that article or thread that talked about ich dying off in an aquarium that doesn't get new additions after 6 or so generations due to attrition or population dying out. Too bad the search engine isn't friendly for weeding through topics that have so many entries... that and I'm not even sure if it was a thread here on RC. If I recall correctly, the reason they were talking about Ich not being seen (even if it is present) in established tanks was because the existing fish had been repeatedly infected and had built up acquired immunity, so that they never really got infected to the level that the parasite could get out of control. And the population would either completely die out, or be so low that it was negligible unless you introduced a new fish that usually gets overwhelmed by an outbreak of parasites. Why would the new fish be overwhelmed? Usually new fish are in much worse health after shipping, being in holding tanks at the store, being stressed out by being put into a new environment, and also because they are then put into an environment where they may be exposed to many more parasites than they were in the wild or in dealers tanks running copper. They get introduced into your established tank that has a dormant ich presence, the ich is able to quickly explode in population on this new fish, and the infection for the new fish is often enough to put them over the edge. A note of caution, putting in a new fish also exposes your existing fish to the already present ich, the new fish can act as a host for an explosion in the population which can then overwhelm the fish you already had that were able to fight off the mild amounts of parasites in the tank without symptom. I think a lot of the people who blame the new fish for introducing Ich already had it, the new fish was just the catalyst/host allowing for a quick explosion in the parasite population of the tank. This is why you see people who went through quarantining new fish still having issue with new fish breaking out in Ich, and then maybe after this they see their existing fish showing slight Ich infections... they jump to the wrong conclusion thinking the quarantine didn't work, and then don't bother to quarantine in the future. Then they get flatworms, or brook, or some other plague
One other comment, even if you don't see Ich on your fish, and the current Ich population is low enough to be fought off by your established fish, if you do have Ich in your tank it is still probably much higher concentrations than that seen in the wild. It is the dilution factor and the amount of Ich in the wild that when it hatches from the cyst or spore stage never finds a host to breed.
In an aquarium, Ich can balloon out of control very quickly because of the limited volume of water, once ich starts to reproduce, many more of the parasites will successfully find hosts and breed again since the fish are in a limited area and can't swim away from the substrate where all the spores go and go to a new part of the ocean.
Cheers,
Doug