Best accuracy -a few questions for the experienced!

[MAKDENTAL]

I have just bought the GHL KH Director with slave doser set and got my first KH readings (now 4 of them at 7.5dKH) loving it so far!

However my Redsea alk test has given me 8.2 (and have used this successfully for over 7 years) for the same times.
I understand that consistency is key here but also would be nice if test of KH director & Redsea were closer together! To this effect I'm going through KH Dir setup up settings very carefully and have a few questions that I feel need addressing:-
Sample tube length: instructions mention adding dose tube length of 12cm to the 4mm (int dia) silicone tube lengths (in my case 29plus 16cm) and adding 7ml for the water filter and obviously de aerating tube. Making in my case tube volume of 13ml

Points to note:
• The GHL Dose tube diameter is much less than 4mm -probably 3mm?.....
• It is impossible to remove all bubbles from the supplied “filter” about 1cm of trapped air, at the same time this trapped bubble does not wander? So 7ml to add becomes about 6ml

My question: should this be taken into account in my case~ 13 ml becomes say 12ml? Or is it already included in the software as I suspect the doser only uses the tube length and a bit more to completely flush the system?

pH electrode calibration does not have any temperature compensation input:- should this be done at room temperature which in my case is 21 or at 25 degrees C which is my Tank water temperature as I do with my Sump pH electrode? I understand that by the time the sample water is drawn up it will be more like room temperature. -IS THIS IMPORTANT?

Can I swap round the stacking arrangement so dosing pumps sit on top of KH Director as in my case easier to have kink/sag less reagent tube?

I have drilled a hole in the Reagent bottle top making it slightly loose with tube to prevent vacuum -will evaporation be a problem at 21degrees over say 3 months?

I use silicone for sealing aquarium rubber gaskets rather than Vaseline -is this a problem?

What do forum members and Vinny think please?

[Vinny]

Hi,

Don't overthink it. :)

Tiny variances of 1mm in tube diameter and tiny bits of trapped air in the filter are already taken into account with each test. Just add the total length of the sample tube, including the length of the filter and enter it into the KHD sample calculator. The key for accuracy will be in how well the calibration is done for the dosing pump heads, especially the reagent pump head.

Room temperature calibration fluid is OK.
As long as there are no immediate kinks in any of the tubing, it will not kink itself.
There is no need for any silicone or vaseline on the tubes.

As for the mismatch in readings between the KHD and RS kit. There are multiple reasons for this. Although they are both testing for the same parameter, the steps used to get to the end-result are not the same. KHD uses lab grade measurement procedures whereas traditional kits use hobby grade practices which are more susceptible to user error.

[Vinny]

For more tips on achieving best accuracy, take a look at our FAQ post:
https://www.aquariumcomputer.com/support/faqs/#1544275617719-e411fbea-c9e7

[MAKDENTAL]

Thanks for that Vinny -Just wanted to be sure -what about reverse stacking so dosing pumps sit on top of KH Director ?

[Vinny]

That is perfectly OK to do. :)