Fritz RPM (Blue Box) fresh mix parameters are off. What's wrong?

[Obriy]

I've got a box of Fritz RPM (Blue Box) and decided to use for QT. I mixed in 5 gallon buckets and, after mixing for about 20 minutes and letting it sit in a bucket for 3 hours, I checked some parameters. They don't match what the manufacturer states on their website:
Alk - their website 8-9, mine test 7.2
Calcium - their website 400-450, mine test 365
Magnesium - their website 1300-1400, mine test 1155
I mix to 1.025 salinity and they provide the parameters for 1.0264 sg mix. I understand that my readings should be a bit smaller, but not that much!
That could be a reason for the discrepancy? If that was only one test, I would question my test kits. However, all three parameters are much lower...

 

[slythy]

How are you measuring salinity?

 

[Obriy]

How are you measuring salinity?

I use refractometer.

 

[slythy]

I use refractometer.

Your happy with the calibration? I prefer a hydrometer. I use fritz blue and only time ive gotten weird values was from a bad calibration.

 

[djf91]

I think hydrometers are known for being the least reliable of the bunch. But I agree, I would confirm that your salinity measurement is accurate. It is a fairly cheap salt mix so it would totally surprise me.

 

[rtparty]

Your salinity is low. Refractometer needs calibration and verification. When the big 3 are all low, it’s almost a guarantee the salinity is low.

Tropic Marin glass hydrometer is the best by a mile.