Calcium that high is a problem. Are you sure the test kit is accurate? What is your alkalinity running? Lots of great links here. This is one of my favorites, but as you can see there is alot of reading there!
Alkalinity is around 9 so should be okay. I use "Prodac" brand salt. Supposed to be one of the best. It does have high calcium but sometimes I register above 700ppm. Not sure what you mean by "dosed"? I use a refractometer to measure levels and am sure it is accurate.
Okay.....water changes are done fortnightly.....about 25%. I use a refractometer to measure salt levels and a PH monitor. The salt level stays pretty much between 600 and 700 and no I dont add any supplements. I mix to about 1.0125.