KH Director problems

[Jubei2006]

Posted this in the general equipment thread and got no real response, so placing it here in hopes of ideas.

So I purchased a second hand KH director, it seems to be working fine except for my KH readings are off from the manual tests I have been using. I changed the lines out, have calibrated the pump head 3 times, just recently changed the KH pH probe and followed the calibration procedure twice and checked with the 4 and 7 pH solution after, and measured the lines properly from the sump. I have primed the lines and made sure there are no air bubbles, and used the KH 7.5 reference solution to ensure the reading should be accurate (my KH director read 7.7 on the 7.5 reference). The problem I'm having is that my KH director is reading almost 1.5dKH difference from the readings of a manual Red Sea alkalinity test (I have used two different lots of the KH titration solution both were within 0.5dKH of each other). My Red Sea test was last at 8.7 and the KH director was reading 10.0. If the 10dKH is right I'm fine with that. Was aiming for 9.0. If it's wrong, then my KH is less than NSW if I let it drop.

 

[Lasse]

If you use Read Sea test on your KH reference - what do you read in that case`? I would use this feature (red marking) for calibrating the KH director if the KH director give you stable readings.

Sincerely Lasse

 

[Jubei2006]

So the Red Sea test came in at 8.7 dKH, the KH director reads 10. I guess I don't want to artificially lower the KH director if it's a true reading (it was within 0.2dKH of the reference solution)? I did mix up some new saltwater for a water change today. So I guess I'll use both the Red Sea test and the KH director to see if they are close to the bag stated measurements or not. Thanks, I'll keep the post updated.

 

[Lasse]

If you use your red sea test to analyse your reference solution - you will have all your answers. IF you are sure on your reference solution - adjust your KH director to show 7.5 and you should be able to trust it.

Sincerely Lasse

 

[Jubei2006]

I have thought about that, but the reference solution is blue, just like the start color of the red sea test, so dont know how easy it'll be to see the quick color change to a green. I'll give it a go tomorrow. Thanks!

 

[Lasse]

OK - Is it GHL own reference solution? If so - I would trust the KH director before the Red Sea test and just adjust the KH director to show 7.5

Sincerely Lasse

 

[Jubei2006]

Was able to see the color change with the red sea. It was about 1dkh off. So I guess the KH director is correct. Guess I'll play is safe and back the KH director down 5% and continue readings from there. Luckily with either test the tank only varies 0.1 to 0.3dKH per day.

 

[Jubei2006]

Thanks guys, have a good weekend.