Epsom Salts are highly soluble so they shouldn't form a crust on the leaves like that. I'm mystified why you have so much crusty stuff on there.
If you have some warm spring rains coming up, be sure to put your orchids out for a good rain water shower, won't you? If you do have a build-up of salts in the medium, that will wash it out nicely. Key word is "warm" i.e. wait until it's over 60deg. or so.
