Ph Probe will not read 7.01 but reads 10.01 perfectly on trident

[14 foot reef]

Ph Probe will not read 7.01 correctly but reads 10.01 perfectly
On the Apex I calibrated with 3 different lots of Milwaukie reagents.
Apex will go through and finish the calibration. As soon as I put the probe 7.01 it reads 6.2 +/- on the three different lots

Tried 2 different probes. both not new but cared for correctly.

Is the Apex the problem or the probes ?

 

[HankstankXXL750]

Don’t know a true answer for you, but I have a Hanna checker that uses 10.1 and 7.1 and Neptune uses 7.0 and 10.0. I reached out and asked them and of course they recommended their solution as it is a different pH so I just ended up buying both for each application.