imo, i would continue the treatment on the fish for three days after the fish are showing no signs of ich. is is a parasite that lives in the water. when it is not on a host fish it can be destroyed. the parasite fisnd the host fish and burrows under the scales to feed. when the parasite is in the fish it will show the signs of ich. the white specks, not eating, listlessness, etc... when the parasite is in the fish it cannot be destroyed. after the fish have showed no signs of ich for three days stop thetreatment. you could also raise the temp slightly to the max that is allowable for the fish. also raise it slowly! you can shock the fish by raising it all at once. also do 10 % water changes daily before adding the medication to the tank. would also not feed the fish. they probably have no desire to eat and all you will do is raise your toxin levels witht he uneaten food remaining in the tank. if you fast the fish for three days or so it will not harm them.
parasites cannot live in warm temps and fungus cannot live in low temps. so if you are experiencing any of these adjust your water accordingly but slowly and then raise/lower it back after treatment.
hth
maggie