I always sweep all the salt crystals formed on my tank brace into the tank. the salt crystals fall on my corals etc no problem.
But I think changing water is totally different. When u change a substantial amount of ur tank water, say 30%, u must ensure the salt is fully dissolved and all reactions have stopped before adding to main tank. If u pour the newly mixed water in straightaway, the exorthermic reactions that takes place will shock the corals.
Try mixing one pail full of salt water. add the salt needed at one go. feel the salt and water. you will feel that the water is v warm and even hot. this is due to exorthermic reactions taking place.
It is probably the stress that induced ich outbreak. these salt crystals cannot logically directly effect an ich outbreak.