problem maintaining proper parameters

[Aquattro]

Evap seems fine, you should be able to maintain levles with the kalk alone, unless you have 40 or 50 pounds of corals in there!!

I think Mg could be a bit higher (1500ppm rings a bell, maybe someone confirm?) but try to use just the kalk for top off. Make sure your kalk is ok by testing it's pH. Saturated solution should be around 12.4

what are your nitrate levels?HNO3 is a weak acid that can affect alk (and therefore Ca). Make sure it's low to non-detectable.