Lately I've been brewing Dunkels with water with 50ppm Ca, about 30-40ppm Na, 50ppm sulfate, and 80ppm chloride, and about 200ppm bicarbonate gets me a mash pH of about 5.55 (that will depend on your specific grist.) I'm really liking the results. This profile is merely the product of doing as little to my RO as possible to achieve proper mash pH and meet my low oxygen brewing requirements for metabisulfite.