A tried but true, and quite effective treatment I might add, is to setup two QT tanks. Day one, fish are in tank A, tank B is setup with clean water at the same temp and pH as tank A. Day two, all fish are moved from tank A to Tank B, Tank A is emptied, cleaned and filled with new saltwater at the same temp and pH as Tank B. Day three, all fish are moved from tank B to tank A, and tank B is emptied, cleaned and filled with new saltwater.
While you will certainly go through a lot of saltwater, you will not have an ammonia/nitrate problem and you will break the ich cycle. This method can be used for oodinium as well, simply add copper to the new water each time. For most folks, a 20 gallon tank works well, though you could go larger if needed. You never worry about interfering with the biofilter because you never allow one to develop in the first place.
Lots of work but always yields success.