Immune fish do not get sick because,,,well,,, they are immune. But immune fish won't stay immune unless, like Brew said, the fish are exposed to parasites, "and" you are feeding them correctly. Flakes, pellets and anything freeze dried is not IMO food and the fish will not stay immune. Food that does not have live bacteria in it is also not the proper food IMO to feed every day.
I use my diatom filter maybe once a year and I don't think I used it in over a year and in that time have added quite a few fish and collected all sorts of stuff from the sea so the diatom is a non issue as far as parasites in my tank go.
I am very sure there are some parasites in my tank, at least I hope so. I am sure they are sampling some slime from my fish until they realize my fishes slime has anti parasitic qualities that prevent the parasite from harming the fish itself. (here is where most people will come up with that silly playing Russian Roulette thing because I can't even speak Russian but did date Russian girl for a few years.)
As you know I run my tank totally backwards from the vast majority of people on these forums but I also have no problems and never have to go on disease threads. This hobby is run on rumors and not even good rumors.
If I were you, and I am probably not. I would be happy knowing some of my fish recovered from ich and are immune, but I would also feed, every day some meaty food such as clams or live worms that have live bacteria in it. Commercially available food is fine especially if it "doesn't" say "Irradiated to kill harmful parasites and bacteria" or something like that. We actually want those "harmful parasites and bacteria". So if you feed commercial food every day, I personally would supplement that with either a few live black worms, white worms, earth worms, Eartha Kit worms or clams that I would buy live and freeze myself. That should keep your fish immune forever and you should never have to go on that "Disease thread".
Most people try very hard to keep parasites out of their tanks. To me, that is totally wrong. Fish evolved with parasites and are fine with them. The parasites make the fish much stronger. You don't want Sissy Mary fish that get sick at the drop of a hat or Oldsmobile tire. You want robust, immune, real Man fish. Unless of course they are girls. Then you want Supermodel fish. :rolleyes:
PS I also would not put any herbal remedy in my tank. I also would not put tree stump remover, prozapro, copper, bio pellets, GAC, hydrogen peroxide, Kick Ick, Rawaphos or any thing besides seawater, calcium and alk.
