I like the Randy's 2 part since it only takes a daily testing of alk to get a daily usage feel. Adjust using an equal amount of the two parts. Then after that, once a week to see if you are drifting up or down. Then each morning I just add the daily amount. If I had a dosing pump, that would be nice but it's not that hard to add a cup or two of each. Then once a month I do a ca and mg test and it's right on for ca but I usually have to catch up a hundred or so on the mg. You also add a cup of mg mix for every gallon of the ca and alk you use.
It's 2.8 dKh for every 10 ca btw.
I use about 1-3 dKh a day over the 3 gallons of kalk I drip a day. That number seems to shift to the higher in the winter months, I'm thinking maybe the warmer tank temps slow down some growth. Also if you add a bunch of corals or sell a bunch, disturb them where they slow down, etc it may take a couple daily alk tests again to re-establish your daily usage. You could use the ca as a benchmark test for daily amounts but that is alot more complicated of a test than a cheapo tetra test for alk. 7-10 drips and done. Maybe it doesn't tell you it's 8.x dKh or or whatever fraction the better ones take it to but it's not that critical to be more accurate. When I do ca or mg or phosphate, since I do them less often, go Salifert.
Another thing that will cause a balance shift is phosban. It tends to bond the carbonate ion so your alk will drop out of proportion. IO has been running about 12-13 on alk when I test it so I never need to bump alk for a water change but I do have to add the ca and mg before I do the water change so it is in balance and I don't mess my tank usage numbers up.
