Long and short is that it includes kalk to maintain levels, while having individual calcium and alk additives to do major adjustments to your tank and water change saltwater. Spend an hour and watch all these videos, it has allot of overlap but you'd have a pretty good understanding. Long and short is to use kalk until your evaporation won't keep up with the needed dosing levels. I would probably start out with kalk and only add 2 part when it is necessary.