UPDATE: May be switching to Salifert, from JBL.
Salifert has released a new freshwater potassium test kit that is not only less expensive than the JBL, but relies upon a color change, potentially providing more precision than the turbidity-type tests, such as is the JBL. Once you start adding the drops, when the potassium level is reached, there is a dramatic change from a yellowish color to a strong blue color, leaving no doubt that the test is completed.
However, when going through the calibrations (details below), I found that adding 50% more test water (7.5 ml instead of the 5 ml in the directions) gave precise readings. This is a little concerning, and provides cause for doubt, because you would think that Salifert would know this …if I were correct. It may simply be that this particular lot is off. I will calibrate the next kit, once this kit is done but, at least, this kit is now calibrated.
To calibrate this kit, I used three K targets: 10ppm, 20ppm, and 30ppm. I added KHCO3 in one-gallon containers of RO/DI water at 97mg, 194mg, and 291mg, respectively. Using a Hanna alkalinity checker (calibrated), I found that the dKH readings were within +/- 5% of the expected dKH for the loadings. Each potassium reading was within 1 point of the expected result.
Last edited by Deanna; 12-15-2019 at 03:43 PM.