Not sure what you’re using your TDS pen for. If it’s for cannabis growing keep in mind you want the EC solution that’s closest to your reading needs.
We generally feed at 1200 - 1600 EC when feeding and mixing or nutrients…
We try to obtain and maintain 2000EC runoff.
This means the closest solution to calibrate would be 1413 us/cm.
If whatever you’re using your pen for has the need for 718us/cm then please continue your search and disregard this post
I don’t know if this will help you or not
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