PH prob

Hey

recently acquired profilux 4, and acquired a second ph probe to control the co2 of the calcium reactor
and installs on the redox port.
I calibrated the two probes with the calibration liquid 7 and 9 without problems.
to test if it was ok I put the probes in liquid 9, but both probes take different measurements and below standards

1 probe read in liquid 9 ---8,75 and in the liquid 7--- 6.82
2 probe read in liquid 9 ---8.82 and in the liquid 7--- 6.80

I have already calibrated several times, I put the liquids at 25º, the result and always the same.

2 weeks have passed and the same happens, the profilux will be damaged??

tanks