I have seen this subject come up many times, so I thought I would share how I addressed the issue. Maybe Randy can confirm that I didn’t make any amateurish errors.
Creating an Alkalinity Standard:
I created an 8.0 dKH (142.88mg/L) alkalinity standard using Biopharm Alkalinity Standard 1000 ppm. Using a class-A graduated pipette with tolerance ±0.1mL, add exactly 14.3 ml of the 1000 ppm standard to a 100 mL volumetric flask. Fill balance of 100 mL with DI or distilled water. Mix, and you are all set. All this stuff is available on
Amazon.
I am not 100% sure, but after some comparison testing including the “Fauna Marin Multi Reference”, it appears this standard reads as 7.8 dKH on the Hanna HI772. In any case, I use this as MY Hanna 7.8 dKH standard, and I am certainly not too concerned if the absolute value is off a couple tenths.
Hanna Drift:
I can confirm the Hanna alkalinity reagent drifts. Aging in a sealed bottle does not appear to cause drift. Opening and closing the bottle 20 times over a period of time appears to degrade the reagent, and cause significant drift as the reagent is consumed. When you open a new bottle, you can sometimes see a big jump in the alkalinity reading.
When I open a new reagent bottle, the first thing I do is transfer the reagent to three 10mL glass bottles (from
Amazon), topping them off to minimize the air, and storing them in a dark place. This appears to eliminate the drift.
Calibrating the Hanna test:
I typically purchase 10 alkalinity reagents at a time directly from Hanna, and hopefully they are all the same lot number. I calibrate the batch with the 7.8 dKH standard, and make an adjustment typically from -0.2 dKH to +0.2 dKH. I have never received a reagent bottle outside their stated test kit accuracy of +-0.3 dKH, so I think I’m on the right road. Bottle to bottle accuracy within the same batch number appears to be excellent, so I only calibrate once for the batch.
This procedure appears to produce repeatable alkalinity testing, without drift. I also have to say that for its simplicity, accuracy, and cost the Salifert test is very impressive.
. It has a PH probe and it adds a reagent (I would now assume some sort of acid) to "somehow" determine the Alk. I guess it adds reagent to the sample until the PH is 4.5 and that would do it. No wonder it calibrates the PH probe with 7.00 and 4.00 fluid.
