Hi Lisa,

Just to second Matthew's suggestion, Si(111) should work fine for Ca K edge.     In my experience,  using high angle makes it much more challenging to keep a stable beam -- roll errors become more important, and thermal load can also be worse (power density on 1st crystal, heating from scattering on the second).

So, in that sense, and if it's an option,  Si(111)  (at ~30 degrees) seems preferable to Ge(220) (at ~50 degrees, I believe).