Sudden change of measured values

[Thornrose]

Hi,
I've had my KHD running for a month. In the beginning I had to re-measure hoses and recalibrate the probe a couple of times to get the values ​​to match my Hanna Checker and Salifert test. Since then, everything has looked stable for about 3 weeks and I was going to go from measurement to control, but all of a sudden the measurement values ​​from KHD dropped from 6.5-6.9 to 5.6-5.9 while the values ​​with Hanna Checker are still around 6.5. Now I have recalibrated the probe and checked for air bubbles in the reagent hose but the values ​​are still 0.5 to 1.0 from Hanna Checker. What could it be due to?

[Vinny]

Sediment, dirty filter, accumulated air bubble now inside the KHD.

The best way to adjust the KHD's final readings is to use the 7.5dkH reference fluid. It will be far more accurate and reliable than relying on the measurements provided by conventional test kits which are susceptible to a larger margin of error.

[Thornrose]

Thanks for your answer.
The filter don't look dirty to me (see video) can it be anyway?
https://youtu.be/yo6C0qGg7Sc

Before calibarting I flushed and emtied the measurement cell. Can there still be air bubbles inside?

If I use the reference fluid, do I adjust by % to get the right value?

Best regards,
Christer

[Vinny]

Hello Christer,

It looks like your filter is missing the directional arrow. Please email us this video and copy of your receipt for further assistance.
sales@ghl-kl.de