The answer lies in your current Ca and ALK parameters and your daily uptake. Test both and use the Reef Chemistry Calculator to determine how much you need to add to reach the desired numbers. You then daily-dose the amounts needed to maintain those values. The type of salt you use and frequency of water changes will also influence these values.

You'll need to adjust as your corals grow and/or you add additional livestock to the tank. For reference - In addition to Kalk laden ATO, I dose ~101 ml/day of each CA and Alk in ~50 gallons of water. This is a relatively large amount for the water volume, but is due to large demand by a high density of SPS, LPS and 2 large clams.