Calibrating 2 of my PH probes

[juboy27]

Hi I have 2PH probes on my Neptune apex system one doing the CO2 ph in my calcium reactor and one doing my tank Ph. Today I calibrated both probes with number four number seven and number 10 calibration solution using Milwaukee. After calibration I've put probes back in the bags the calibration bags to check they were okay I've put both probes in my sump and one was reading 8.11 and one was reading 7.87 which is a big difference. I redone the calibration and ending up with the same results with both probes in my sump I cannot make out what is going wrong or what I am doing wrong can anyone please help me or suggest anything
Thanks


Sent from my iPad using Tapatalk

 

[hijinks]

are they in the same chamber and close to each other? If one is in the incoming chamber from the tank it might have a different ph then a probe after the skimmer which will release co2 in a different chamber of the sump