Well, I started adding vinegar tonight. I added 4 teaspoons of kalk + 120 ml of vinegar to my 6G top off container. It should drip slowley over the next three days through the top off float valve in the sump as the tank water evaporates. I measured my tank params before I started as a reference:
nitrates 20 (I can't tell whats causing this to rise)
Ca 375
Kh 8-9
PH 8.2-8.4

I will update the thread with more params as time goes.