Yes, Paul, dripping kalk is a much better solution than either baking soda (bicarb) or anhydrous baking soda (sodium carbonate), HOWEVER, his indicated Ca is around 500 - and kalk will increase that.

I still think the thing to do is this:

Increase aeration/surface water flow (to blow of the CO2) and,

CHECK THOSE TEST KITS! I really think he'll find that he has a kit error somewhere...

BTW, many times, the BEST solution is big water changes.