I have a 75G with a 15G sump, mixed reef, softies and LPS and fishes. The best thing I have done in the past year was to get two paristoltic pumps from BRS. Manual dosing is not the way to go.
My Alk usage is generally greater than my Calcium usage, but it all depends on your mix of livestock, I am sure. With the basic pumps from BRS there is no adjusting the amount dosed by the pump; it is either on or off. So you would get two timers (one for each pump) and set them to go on as needed. As a good guide for you (since our tanks are similar size - again, depending on your livestock load) I have my Alk pump go on twice a day for about two to three minutes each cycle, and my Calc pump going twice for about five minutes total. Simply run a hose from 12-oz plastic bottles filled with the two-part system (one bottle per additive) to the pump, then out from the pump into my refuge.
Start low dose to begin, and test daily making time adjustments until you get the readings you want. Don't really see too much change with water changes. I only dose Mag. on an as-needed basis, testing for Mag twice a month, and testing for Calc. and Alk. once a week.