You may find kalk to be enough. If not as Gary suggests you can tweak with 2part.
Calcium is ok north of 400. As long as you keep it over about 400ppm stability is not very important.
Alkalinity should not be allowed to shift more than 1 dkh per day. Sps can be very sensitive to alkalinity shifts. Alkalinity also depletes quicker than calcium. For every 20ppm of calcium used in calcium carbonate precipitation( growth of coral skelton, coraline, etc.) 1 meq/l or 2.8 dkh of alkalinity(carbonate) is used. Daily additions of alkalinity are quite common.