I am trying to setup a new KH Director unit. After working on it for the past couple of days, I am able to get it running on a stable basis. However the KH measurement is showing up in 11+ whereas my Hanna meter shows around 8+. I ran the measurements multiple times back to back it is showing 11.4, 11.6 etc. which means that the KH director itself is working fine. I am trying to eliminate few other factors that might affect the measurement.

I measured the tube from the sump to the doser and it is coming to 66.5". Add 4.2" of silicone tubing in the doser and another 6.3" of tubing that goes from doser to director, it gives me a total of 77". If I enter this it gives me 24ml of sample water. This is what I used for few tests. Then I separately measured the water from the tube for the entire length using a graduated cylinder which showed me there was a total of 21ml of sample water in the tube. I tried both numbers and the difference in KH is not much different. They are still in 11ish range.

The other thing I noticed is the pump that pulls reagent stops in between for a brief moment as it pulls the reagent. See here for a video .

Is this normal?

I took the electrode out and tested by placing them in 4 and 7 reference solution and they are within acceptable range. So I ruled that one out.

What else should I be looking for to get an accurate KH result?