following taken from reefkeeping mag...
"Some individuals prefer to use freshwater with methylene blue in the dip (Fenner, pers. comm.- more information here). Methylene blue is an anti-microbial dye. It is effective against a wide range of microbes such as bacteria, fungus, yeast, etc. This combination works well to rid the animal of external parasites and provides some protection against secondary infections. As I stated in part one of this series, I almost always use daily water changes. These daily cleanings tend to spur the fishes' own immune system to combat any secondary infections by helping to maintain optimum water quality, so I have not felt the need for using Methylene blue, but it is a worthwhile option to consider."