Hanna calcium checker help

Dave Clark · Nov 21, 2023

Reef Devils said:
I sometimes use RODI with no problems

Randy's post implies that the checker gives inaccurate readings if the blank contains very small levels of calcium. I was wonder if he considers the checker to give accurate readings if the blank contains even smaller (or no) calcium.

I'm asking this because I've seen other people insist that the checker is inaccurate regardless of the quality of the blank.

Salty_Northerner · Nov 21, 2023

The only ppl that complain about the checker are ones that either don't follow direction or just have a hate on for Hanna. Ime it's quite reliable and had never steered me wrong. Distilled water is a good choice as well as RODI if you know the system is pulling out all the Calcium. These are hobby grade and get you in the ballpark.

Randy Holmes-Farley · Nov 21, 2023

Dave Clark said:
Randy's post implies that the checker gives inaccurate readings if the blank contains very small levels of calcium. I was wonder if he considers the checker to give accurate readings if the blank contains even smaller (or no) calcium.

I'm asking this because I've seen other people insist that the checker is inaccurate regardless of the quality of the blank.

I do not recall seeing a real examination of its accuracy, but the number of folks that have issues with it is seemingly high.

IMO, the issue of calcium in the blank is due to a poor design. The use of only 0.1 mL of tank sample diluted into 10 mL makes the possible calcium in the blank much more significant than if there was more sample and less distilled water.

It also puts a big premium on accurate measurement of that 0.1 mL If you actually dispense 0.095 mL instead of 0.100, which is likely well within expectations, then 420 ppm calcium will read as 399 ppm, even without any calcium in the blank causing issues. IMO, it is easier for a kit using 2 mL of tank water (such as salifert) to get an accurate volume measurement than one using 0.1 mL, but I freely admit that I have not seen an analysis of the sample volume actually used for either one.