The following info should help everyone mag stir or powerhead stir.
You use your reactor to replace evaoprated water. Thus you should know
1) The volume your nilsen holds
2) How much evaporated water you have to replace
3) How high the kalk cloud rises in your mixing cylce
All the CLEAR saturated kalk effluent rises to the top of the reactor leaving the undissolved kalk in the bottom of the reactor.
So thus if your kalk cloud rises 1/3 of the way up your reactor during the mixing cycle, once you dose 1/3 of your reactor volume you need to mix. Thus if your reactor holds three gallons, and your cloud rises 1/3 the way, for every gallon you dose, you need to do a mix.
You really have to figure out how long your going to run the mag stirrer to figure out how high the kalk cloud goes.
In the powerhead models, the intake on the power head is set at a specific height so that you always know how high the cloud goes.