ffsteve
+1 on above with proviso
some tanks can be maintained using Kalkwasser alone
but there are tanks, with very high demand, in which even super saturated Kalkwasser would not be able to keep up with demand as the corals grew in terms of size, and in terms of your stocking capacity
if it is a predominately soft coral aquarium, that you are just building up the stock in, then water changes alone with a salt mix, that has the levels you need is often enough
if its a developing aquarium with some SPS, or clams etc but still mainly soft corals, you may be fine with a weaker than full strenght Kalkwasser solution to maintain those 2 parameters
with Kalkwasser another limitation is your evaporation rate, if you live in a climate where evaporation is limited, then you may not be able to sustain the needs due to inability to get enough Kalk into your set up on daily basis
in situation like that 2 part dosing of Ca and Alk solutions may be an additional requirement simply as they do present a stonger solution ( more delivery for less volume of fluids utilised)
Steve