People consistently say to let the tank lay fallow for a month or so, reasoning that all the ich parasites will die in a tank without hosts. If this procedure is not performed properly, and you reintroduce fish that have been treated and are now ich free, the ich can at any time "come back" and reinfect the fish. The conclusion is that a tank is never cured of ich until you let it lay fallow for over a month.
To me, at least on its face, this argument is flawed. If it were valid, ich that has "fallen off" the host fish cannot come back to reinfect the host fish after ~ one month's time, as a matter of fact. Sure, during that one month it can, thereby perpetuating the cycle, but not after that. Ich cannot "come back" six months later. If it could do that, then letting the tank lay fallow would be useless. Whether the tank is fallow, or whether the tank has healthy inhabitants that are not infected by ich in the water column, the result must be the same: the ich must die within a month of having no host.
I think that there is something else going on here, namely that some ich can survive for much longer than one month without a host. This proposition is supported by the anecdotal evidence of people letting their tanks lay fallow for upwards of one month, reintroducing "cured fish," and having ich strike again. Certainly, some of the people that testify to having this experience probably did not follow the quarantine procedure correctly. However, I think it is unlikely that EVERY SINGLE person who claims to have had this experience did not follow the procedure correctly. I think it is far more likely that we don't completely understand ich.
I also think that this viewpoint is reflected in the alternative treatment strategies that people are increasingly employing, particularly boosting your fish's immune system through clean water, good food, and medication. A well fed fish kept in clean water and in a stable environment should be able to fend off ich by itself. As everyone knows, the fish becomes susceptible to ich only when its immune system is compromised. In fact, this method becomes even more effective if all the ich actually does die within a month, because in that case, if you keep your fish healthy for one month, the ich is going to be gone for good. However, as I suggested earlier, I think it is more likely that ich is not necessarily gone after one month.
Moreover, if ich can live for over one month without a host, and a compromised immune system is a necessary condition for ich "infection" then other treatment strategies seem counterintuitive. In many cases, removing a fish from the display tank, and putting them in a small quarantine tank with copper, or in a hyposaline environment, is going to stress them out even more. Consider also, that these quarantine tanks are usually set up "on the fly." They are probably almost always undersized, and they have not gone through the nitrogen cycle, so your dealing with ammonia problems. Moreover, you must strike a delicate balance between causing an ammonia spike and feeding; remember, a fish that is eating alot is a happy fish. However, it is very difficult to heavily feed a quarantine tank. The worst part about all of this is, then you return a supposedly "cured" fish to a "fallow" tank. However, what you are really doing is returning a fish whose immune system is not in tip top shape back into an environment that probably still has some ich left. Not too mention the fact that if you have a larger display tank, returning all the fish is probably going to cause an ammonia spike anyways. If that one month of fallowness killed all the ich, it certainly had a detrimental effect on the beneficial bacteria population in your tank, which had to go without a nutrient source for one month.
So, I submit, that for all but the most diligent hobbyists, maybe rehabilitating the fishs' immune system is a more effective and practical treatment then the hospital tank method.
Let the firestorm begin...lol.
hope this helps.
