The majority of my topoff is Kalkwasser. During the summer time I may got through over 35gallons of water a day. The majority is Kalk. If the system pH is too high the RO water is diverted past the Kalk mixer. I used to believe that I only needed to add Kalk to the mixer when the slurry at the bottom was depleted...So I would add Kalk every 4-6 months. I learned this was wrong. There is lots of 'crap' left after the Kalk is mixed in solution. I added a pH probe to the Kalk mixer, and now I know when to add additional Kalk. In the winter time it's every 2-3 weeks. In the summer time with bigger evaporation number its every 10-14 Days. Each time I add Kalk I am adding 4-10 cups. I have a custom Avast Kalk Mixer which is almost 10gallons.
I use Calcium Reactor 24/7. Adding a pH probe into the Reactor helps dial it in quickly and more importantly lets me know right away when the Rx is clogged, out of CO2 or out of media. All my equipment is outside, so I don't 'check' it regularly.
Adding both the Kalk and Calc to the Apex with pH probes was a huge step in making both devices more stable and reliable.
Dave B