from my understanding it's just a matter of using the 7.1 solution to provide your offset with Salifert. So if you're consistently measuring 2.1 dkh high on the 7.1 solution, then you just have to calculate your offset as CJ said. That's what I do and never had a problem- but I admit I just use salifert because I do, haven't ever really compared against others, so thanks for this write-up!
Is that how you do it? Because I thought you figure out what multiplication factor you'd use instead of 16, to get 7.1 instead of 9.2
Example: My current Salifert alk kit: I tested a standard I made at my work which is at 16.6 dKH. I also tested it diluted 1:1 with DIwater. It turns out I need to use a factor of 14.56 instead of 16 to get the proper numbers of 16.6 and 8.3.
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