ok than it's MG def caused by your water. Especially if you experienced this in another grow. From the xshoot guide in this forum:
"If the starting water is above 200 ppm, that is pretty hard water, that will lock out mg with all of the calcium in the water. Either add a 1/4 teaspoon per gallon of epsom salts or lime (both will effectively reduce the lockout or invest into a reverse osmosis water filter."
Other than that anybody else? I pulled my last post because I misread your post and thought your bad leaves were just on the top!! My Bad