Originally Posted by
samwise
Hi,
Unfortunately I need to report the similar behaviour of KH director, something that makes "adjust displayed measured value " correction hard to use. Specs of the installation below:
- Reagent tube length 70cm, using the one which came with the 3x1000ml reagent set
- Total sample tube volume 27ml and testing volume 80ml
- pH probe double calibrated and afterwards tested in calibration fluids to give exactly 4 and 7
- Flowrates have been triple calibrated for sample and reagent (37ml and 4.8ml/min, respectively)
With this setup I do get consistently low values. I have been now repeatedly testing ATI reference solution (7.5 dKH) and my aquarium system water (as drawn from quite sump region). I have tested everything with Salifert KH test as well.
Reference solution (7.5dKH)
Salifert: 8.3 dKH
Director: 6.3 dKH
Aquarium water:
Salifert: 6.1 dKH
Director: 5.5 dKH
All tests have now been done triple over couple of days. Aquarium test results naturally vary a bit as there is very heavy use of alkalinity. However, same tendency continues. Director gives constantly low values, and it seems, Salifert goes over. Where is acceptable truth... that is troubling. Most troubling is that director is off by (-)1.2dKH when compared to reference solution. Is this just something to be accepted and put like +19% correction into the GHL control center which means that reference solution would give 7.49dKH. Problem is that Salifert and director seem to differ more if the sample to be tested has higher KH. If I implement that +19% into GHL control center and test aquarium water director would give 6,5 whereas Salifert gives 6.1... meaning that correction would cause director to shoot over even Salifert which otherwise always seems to go over. Therefore... what would be reasonable correction if one cannot deduce it from reference solution?