I would say contnue water changes. You will probaly need to do more than just a few 15% water changes. maybe a pair of 50% water changes.
In theory two 15% water changes really does not work out to 30% of teh water volume changed. Its more like 20% or 23%. I think there was some major formula for figuring it out but its above my febel mathmatic mind.
how where you adding your kalk
. I find it best to use a drip line as its easy to control the drip rate with an airvalve or a knot tied into the line.