ya i'm with bebo. You dont need kalk. And i also agree that it doesnt matter what salt you use. Some are better than others yes, but thats cuz the additives in them (some add all the elements, some add 1, some dont add any). The salt itself is the same...just like motor oil. If you go to walmart and get a bottle of the stuff, and then go to checker and get one, the only difference is name...same oil, but each brand/company will add their own detergents to the oil.
Same thing with salt...same thing, they just add dif. additives...some will keep your levels higher/better for longer, while others wont, and those are the ones you'd have to actually dose something if water changes arent cutting it.