basically,
the main difference is...you can only use as much kalk water as you evaporate. if your evaporation rate is high enough that your kalk can keep up with your tanks demands, then that is all you need.
if you do not evaporate enough water, your kalk cannot keep up with your tanks demands, then you will either need to supplement the kalk with another additive, 2 part, what have you....or....
use a calcium reactor, which you can adjust/tune to meet the needs of your tank.
gotta go to work now, i'm sure someone else will chime in if you have more questions.
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