Don't mess things up by trying to achieve a number like 450 just because you've heard that is a good place to be. If you system looks happy with what you are doing, you're just as likely to cause problems trying to force it upward.
Shoot for stability in Ca/Alk/Mg. With a Kalk based system, you are likely to need to dose Mg somehow. Increase the Kalk only until the Ca/Alk is stable (not falling). If your growth (demand) increases, you might have to adjust your Kalk input to match.
In my experience, you need to isolate evaporative replacement from Kalk input. As evaporation changes all the time, you don't want your Kalk input to be also changing. I think Kalk for evaporative replacement works well if you also have a Ca reactor running...but if Kalk is your primary Ca/Alk replacement, you want to control it's input as much as possible.
That's my $.02 worth from running a Kalk-only 30 gallon SPS based system for a few years now. My Ca rarely every gets higher than 385.
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