Inadequate flow could possibly lead to water quality issues then to stress for the fish.
You need to share more info about your tank before anybody could possibly pinpoint your issue:
What size tank?
What do you feed, and how often?
List tank mates, ammonia, nitrite, nitrate levels.
Do you have an appropriate amount of hiding places in the rock for your stock?
Are you noticing any aggression in the tank?
, the best thing you can do is keep the stress level as low as possible and make sure the fish continue to eat quality food. Don't bother with stressing the fish out more by catching it and quarantining it. It is your tank that is compromised by Ick not exactly the fish. What you see on the fish is only a short part of the parasite's life cycle.