Ick does not appear and disapear. It is actually the natural cycle. When was the last item introduce? Fish or otherwise?
The time the trophont
takes to grow is about 24-48 hrs before it becomes visible. After that it leaves the fish host and attaches to the substrate or other hard surface where is form a cyst know as the tomont
. Once the parasite multiples it leave the cyst and becomes the free swimming theront
If a fish is introduced at the last stage, even if it were only one trophont
it will infest the tank and could take up to a week before it becomes evident.
I hope you have a QT ready. Wether it be C irritans
you must treat all
the fish using either copper or hyposalinity
. You need to leave the main display fallow for 4-6 weeks.
Because of the apperant "quick" loss of one tang already, I would go with the copper.