KH Director readings are not staying consistent...

smartwater101 · Oct 14, 2019

So I did 3 Hanna checks. 8.2 8.2 8.2 and a Red Sea to confirm 8.2... The KHD is not correct but is giving a consistent number for 4 tests, so I use the % offset which doesn't seem to actually work properly so I have to just guess several %numbers until the offset finally reads 8.2... 8.2
Re-check with all three... 8.2 yay! Re-check again with KHD because I'm crazy and want to make absolutely sure... 8.2 YAY!!

So I set up some dosing overnight since 8.2 is lower than I'd like. I get up this morning:
3 Hanna checks: 8.6 8.6 8.6 and a Read Sea to confirm: 8.6
KH Director... 8.3... 8.4... sigh

I thought I had nailed it last night! I re-calibrated dosing pumps, I double checked the tube length. The only issue I was having was the % offset which was straight up wrong. (Unless the online percentage calculators have been lying to me for years.) But even that I managed to finesse and get the proper result test after test after test. Everything was on point. I don't know where to even start now... and yes, a .3 difference is a big deal. I want to be able to set-forget, not worry about it drifting, and simply confirm results with Hanna from time to time. If its already drifting within 12 hours....

Vinny@GHLUSA · Oct 14, 2019

The results you're getting are within the tolerance range of the KHD, +/- 0.2 dkH

Keep in mind the checker and KHD do not use the same measurement practices. KHD uses more strict and accurate guidelines which rule out the common factors in manual testing. It is not an apples to apple comparison. The checker is also known to give higher than normal readings which may come from older reagent powder being used.

Your past KHD results are also showing that they are consistent with each other because it falls within the tolerances as mentioned above.

smartwater101 · Oct 14, 2019

Vinny@GHLUSA said:
The results you're getting are within the tolerance range of the KHD, +/- 0.2 dkH

Keep in mind the checker and KHD do not use the same measurement practices. KHD uses more strict and accurate guidelines which rule out the common factors in manual testing. It is not an apples to apple comparison. The checker is also known to give higher than normal readings which may come from older reagent powder being used.

Your past KHD results are also showing that they are consistent with each other because it falls within the tolerances as mentioned above.

So, running the 7.5 dkh reference solution is prob the best way to confirm the KHD is on track?