This is just my opinion. I have had this problem on more than one occassion - which may mean I am dumb. I do not claim to be an expert, just sharing what I have seen, read and tried.
The life cycle is suppose to be about 4-5 weeks. ICH is not suppose to be able to stay alive (continue the cycle) without a fish host, ICH is not "always" there it is a parasite that may become a problem "if present" when the fish become stressed for some reason - water quality, introduction of new fish, water temperature, etc.
Garlic - said to stimulate appetite, no evidence (I have read) that it does anything to prevent/eliminate ICH. Who knows, bunch of people seem to believe it works (a couple from this group who I ask all my questions to).
UV - obviously may kill free swimming stage parasites, not likely to hope for all to travel through that little piece of hose since they are in rocks on fish, continuously multiplying. Perhaps a good way to minimize an out break and give other remedies or the immune system an opportunity to be effective. Again the opinions vary - this is my own.
Tank treatments - people will bash the No sick fish or the ICH KICK or whatever and say they also do not work.
What I think............
I do not think it is always there or in the water.
I do think that if you QT you can prevent from introducing.
I do think that the use of a UV can minimize, not eliminate.
I do think cleaner shrimp and fish can help but only in a situation in which ICH is living in the tank = no outbreak, just small flare ups. Once they have it big, cleaner shrimp/fish are of no value.
I do think garlic stimulates the appetite and good eating fish are healthier, as is their immune system.
I do think ICH can live months and months in your tank without there being an outbreak (big) if the fish are healthy.
I do believe you can starve ICH out of your tank if you remove all of the fish. Time? - - They say 6 weeks.
I do think that if ICH has been living in the tank and then some sudden change occurs creating stress an outbreak can happen.
I do think think a fresh water dip is a good plan, but only due to my poor results performing them. It seems to create a great deal of stress to an already bad situation.
I think in a FO tank that if you keep the salinity low and the temperature higher, you can kill off ICH.
I had a situation similar to yours in which I combined fish from 2 tanks and had an outbreak. I am certain that ICH had been living in the tank, the stress/fighting caused it to become an outbreak. So from my experience I believe it can live perhaps undetected or in small quantities for several months. I want to say 12+ but I just can not say that I did not add rock or coral that may have been carrying the parasite.
As for reeftank tank treatment, I used ICH KICK once in the past and the ICH went away. I used it a second time, double treatment, the only thing that went away were my shrimp, crabs and several fish. I also used NSF when my double treatment of KICK ICH or ICH KICK did not work the second time. I had a rabbit fish and purple tang in bad shape that cleared up.
Was the clear up the first time due to the ICH Kick treatment? Was the clear up the second time due to NSF?
I do not know, do not claim to know, just telling my experience.
Perhaps like a UV the tank treatments killed the swimming cycle, ending the cycle - perhaps it was something else.
Good luck to you - hope this helps.
Thats all I got on this.
(I still don't think it was related to the ich). I had not had a problem with either tank before I combined them. I also did a water change on the tank at the time of combining the two tanks so the ich must have been in one of the tanks and just the stress of adding a couple fish and some rock from the 20g plus the water change must have just been too much. I'm just going to put my tank on cruse control and maintain what I have till the house is finished. I have 2 more maybe 3 large tank projects comming this fall. I'll start a new thread to tell you about those and get input on them.
