When I first started keeping reef tanks 20+ years ago I dosed a two-part solution for calcium and alkalinity supplementation. I figured out what I needed to add and dumped each solution in manually at different times during the day. Was it a pain in the ass? Yes, but reliable automatic dosers back then were just not available. Eventually, I purchased a medical grade dosing pump but that proved to be unreliable, leading me to switch to a calcium reactor. The calcium reactor served me very well over the years since it was pretty much a set it and forget it piece of equipment. Every six months I would change out the media and maybe 1x a year I would re-fill the CO2 tank.