Ph reading, which do I trust?

[diablo243]

Ok so the other night my power heads shut down and at some point the hose fell off the return pump so bad luck all around. Had a PH crash 8.3 to 7.8 and noticed some rapid die off on a Stylo frag. All pumps are running again and water circulating, added an air stone to sump for the time being and see the ph levels coming back up. So the question is I have a Reefkeeper ph probe that I have calibrated but it has always run significantly lower than the API ph test I do manually. When I got the RK it was new but the probe was not fully submerged in solution in cap (maybe evaporation as someone had the kit for sometime sitting in a shelf) question is what do I trust? My API kit was solid at 8.3 but probe was always at 7.5ish, with the drop my API kit went to 7.8 but the probe only dropped to 7.3. Tank and Stylo were thriving until the yesterday when ph defiantly crashed some but between the 2 sources what is more reliable data? Thanks

 

[twilliard]

At that point I would trust the api

 

[redfishbluefish]

Soak the probe in vinegar overnight, rinse, and re-calibrate.

 

[Salty1962]

Does your probe read close to the 10.0and 7.0 test solution? If so then your probe is good. I always double check mine while I have the solution out.