No way do you have calcium in the 800 range; it's simply not possible at anything close to normal ph. Besides, KW does not increase calcium that much, and it definitely does not lower carbonate hardness. The real danger with overdosing kalk is a ph spike.

It really sounds like you need to invest in some new test equipment; Salifert for calcium and carbonate hardness, and a hand held ph probe with calibration fluid. Start with this step; until you really know what your readings are, you can't really do much except maybe make it worse.

If you dosed a couple of gallons of KW into a 150 gallon system over a couple of days, that's not overdosing as long as it went in slowly; I used to dose 2 gallons a day into my 45 breeder. Kalk powder is not particularly soluble in fresh water, so the KW reaches saturation and there's usually left over powder on the bottom of your top-off tub.

Get a ph probe!