In a more established aquarium, it may not even maintain it. Just like a calcium reactor or pretty much anything for that matter, the real issue is what the draw is from your tank whether or not you will be able to raise it, lower it, or keep it the same. If you add enough to raise your entire tank by 20ppm, and the draw on your tank is less than that, naturally your calcium concentration will increase. Conversely, if you have a high draw tank, and dose enough to raise it 50ppm but the tank depletes 60, you'll lose calcium concentration. If it magically maintained whatever number you were targetting, everyone would start a tank at 420ppm, then just use kalk. Eventually, a higher draw tank will probably NEED to add a calcium reactor because you just cannot add enough kalk to get your levels where you want them to be. I have a lot of small-medium SPS and LPS colonies in my tank (probably on the order of 40 different types) and my kalk reactor is enough to maintain the system for now, but I also add an average of 2 gallons per day in kalkwasser.
As far as the magic amount to add, its somewhere around the amount Matt mentioned. If it precipitates out, that's just basically another way to say that the water has reached its carrying capacity for that substance. I add a few cups to my reactor each month, and that keeps it going, but a reactor works by creating a slurry, and pulling out water saturated with kalk, while leaving the supersaturated stuff still in the reactor chamber. For your purposes, just figure out how much kalk you can add to x amount of water and then SLOWLY drip it into your tank. You definitely do not want to dump 1 gallon of kalkwasser into your tank all at once, you'll shock the system. on a tank your size, I'd probably add it over the course of 3 hours (at a minimum), more if possible.
