What to do depends on the severity of the infection and whether it is escalating or constantly at a low level. Also, are all fish affected or only some?
I case of a low level Cryptocaryon infection that only affects a small number of fish I would just wait it out. If one fish is particularly affected you may want to remove that one and treat it in a hospital tank.
I had a very low level infection in my 200 gallon 4 tank system and followed that approach since treating the fish in hospital tanks was just not an option (too many fish which would have needed separation or would have needed live food).
It worked as all of my fish had acquired various degrees of immunity.
It took about a year, but by now it has died out.
This may not work for everyone, and especially not if tangs are involved, but it is definitely an option I would explore before putting a large number of fish through treatment in barren tanks while trying to eradicate the parasite thought a fallow period in the DT.
I rather feed the fish well and let their immune system take care of it.
Of course, if you have an escalating outbreak where every wave is worse than the previous, you will have to treat the fish, ideally all, but at a minimum those fish that are sick (= too stressed or too weakened to build up immunity). You may also want to identify what stresses the fish.
My preferred treatment against Cryptocaryon is hyposalinity - so far it worked every time I had fish that needed treatment. TTM is ideal for new acquisitions to eliminate any hidden Cryptocaryon infection before moving them into the DT, but it is generally not a good option if a larger number of fish need to be treated.
As for garlic: it is completely ineffective against any parasites and also does nothing to boost the fish's immune system. For helping the fish building up its immune system, mixing beta glucan into the food would be a much better approach.
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