You should read about the ich cycle [if you havent already] and find out the appropriate time to end the treatment, according to when it all will die off. Do the longest reccomended amount of time to be safest.
Was this medicine reccommended by a credible fish store? Im asking as I do not know about this particular medicine. But if it is a copper treatment, you need to be testing the copper level in the tank to keep it stable and make sure it doesnt go below the reccommended concentration [because it may not work], or above [because it can harm fish]. If it is not a copper treatment, and doesnt end up working, then try Cupramine.
Do you have a quarantine tank? If not, this is the most effective way to prevent ich, as it allows time for the new fish to become acclimated, gain strength, get rid of stress, and therefore makes them less susceptible to any disease that they may have been exposed to. During quarantining, it is important to watch the new fish every day and make sure they do not show signs of whitespot. And if they do have it, treat ASAP.
