You should first establish a benchmark, so I would start with my WC routine, since that's when you'll be replenishing much of your Ca, Alk, and Mg. Use a good calibrated refractometer or probe to get your salinity to 1.026. Once you have your salinity right, then test your Ca, Mg and Alk, using a decent test kit, i.e. Salifert, Elos, Red Sea Pro, etc. I would do a couple/few WC's to get these param's established and then write down your readings over a period of time to determine your systems needs. Then divide that by the number of days to determine your daily dose.