gypsum is calcium sulphate (I think) . 125 ppm calcium may be what many would recommend , I think a little too much for a lighter ale . It's never an easy answer , all depends on lots of things and what you want out of it . When you look for the ideal water profile for brewing it can vary from info to info and from style to style so I'm a fan of less crap in my beer the better unless it is doing something useful . There are some interesting pod casts on itunes from beersmith that are worth a listen , some cover water profiles and treatment .