It depends on what type of fish and set up you have. Tell me more about you set up.
If the animals in you tank will tolerate low salinity (15ppt ) for an extended period of time that this is the safest way to deal with it.
There are also medications that can be added to the water, but many inverts will not tolerate these treatments. The animals that are effected by the parasite can and should be moved to a quarantine tank and treated there.