I've noticed that at the tip of the dosing line where kalk leaves the doser and drops into the tank, there's always a build. Does this samething happen inside the lines too?
Not as much. The most build up is where it interfaces with the air. But it does build up. The flow is so slow that it takes a long time before it will be restrictive but replacing every 6 months is a good idea. I think that 6 months is what my calcium reactor manufacturer recommends for the final tube.