KHD sudden and inconsistent measurement values.

[mlandscape]

Since new and after just over a month of fairly consistent measurement values without using control, I got an alarm saying the measurement failed due to titration taking too long with an alarm for fill level on Pump 2(reagent). After ensuring that tube was submerged in reagent properly I retested but it failed again for the same reason so measurement turned off until the dosing pumps could be checked. The following day because the doser was bought used I changed Pump 2 internal tubing, blue lid, rollers and rollers holder and it still failed after retesting. Although tubing seemed to be in reagent and drawing decided to change reagent bottle to new bottle even though original still had approximately 250 ml left. After that and resetting refill level the alarm stopped and it worked OK although still seemed to take a while and recorded a measurement of 7.9 down from 8.3. Also, adjusted doser inner tubing on Pump 1 which seemed to have slipped recalibrated from 40 to 36 ml per minute and also Pump 2 from 5 to 6ml per minute.

After recalibration of Pumps, 1 and 2 the measurement was 15.9 !! and subsequent measurements in the 9’s and rising so changed pump 1 speed back to 40ml per minute from 36 ml and pump 2 back to 5 from 6 ml per min. These were the settings pre-alarm and measurement failure.

Due to large variations in measurements (see attached screenshot) I decided to recalibrate all 3 pumps again and came in at pump 1 36 ml per min. pump 2 at 6 ml per min and pump 3 at 36 per min so used those. Following this I completed a new measurement at 16 !!!!! and so decided to recalibrate electrode which checked after gave 7 and 3.97 in the PH solutions. Carried out a further test which gave a measurement of 10.3. Subsequent readings have been 10.8, 10.7 and the latest 10.5.

The month-long consistent levels since starting have all been around 8 to 8.4 so I have concerns that the current measurements are not being recorded accurately. There have been no changes made in the aquarium.

At the same time as the 10.5 reading from the KHD I took a measurement with my Hanna Checker which recorded 8.7. Previous comparisons between KHD and Hanna have been no more than 0.4 difference hence my concern with current KHD measurements. I know that I shouldn't compare these but I just had to check it out.

I have also noticed what I believe to be a strange noise coming from the KHD when the reagent is being added. Seems noisier than before and making gurgling sounds.

Any comments/ advice would be appreciated because at the moment I have lost confidence in the KHD.

Screenshot 2020-05-26 at 12.46.26.jpg