the ich is caused due to bad water conditions(hav u cycled ur tank?).u should use the medicine as per the instruction on the label.please do not overdose!do a partial water change every day(or alternative days) still the white spots completely cures.dont empty the water completely to clean ur tank.if u want to clean ur stones and gravel then store a little of the water from the tank saperately and after cleaning the tank pour back that water.whats the size of ur tank and how many fish do you have?a minimum of 10gallons is required for a guppy.overcrowding also leads to bad water condition.get well soon!!!!!!!!!