Yup, it is not eradicated. It is called "living with ich." Bottom line. Unless you have 3 to 5 tanks setup to qt inverts, corals, fish, LR, and live sand. Ya gonna have ich most likely.Vitamins in food is not a cure for ich. Just because ich is visible doesn't mean its eradicated, it means its managed which in this case I agree that vitamins will help manage ich. Any stress introduced to the tank will let ich pop up right again. Also vitamins will not increase the slime coat of the fish, it will help restore it to natural levels.
Increase the slime coat is not to be picked apart. If it is low. Then any form of increase. Is an increase. Whether it gets back to the natural state or not.
No one said "vitamins is the cure."