How do you mix up your ClorAm-X stock solution? There aren't even dosing instructions for dechlorination on the jar or website.
The directions on the back and from Seachem aren't to be trusted.
I measure dry dechlorinators using a semi-analytical balance with a readability of 0.01 mg and repeatability of 0.02 mg. It has an internal calibration mass but I also check it with a set of Class 0 and Class 1 calibration masses. If I put a 1 mg calibration mass on it, it will read 1.000 mg.
Liquids are measured using micropipettes and calibrated gravimetrically using the aforementioned balance.
Chlorine is measured using
the same equipment water treatment plants use.
I've developed a strict procedure where I weigh or measure out small amounts of dechlorinator and use it to incrementally dechlorinate my tap water. That generates a graph of dechlorinator dose vs. total chlorine whose slope is essentially the "concentration" of a dechlorinator in terms of mg chlorine per mL or mg of dechlorinator.
The numbers provided by Seachem are complete garbage. Any calculation relying on those numbers are also garbage.