pH probe calibration issue

[Infinitereef]

I had my AC jr and the lab grade probe for about 6 months. It was reading fine before until recently when I calibrated it with the 7 and 10 solution. Since then the reading is off by 0.3??

To be sure, I use Salifert and Seachem test kit to verify and both are reading around 8.15 while my Ph Probe is readin 7.8?? I also re-calibrated twice again with 2 additional set of the 7 and 10 solution and the result the same.

Does these probes gone bad so quickly?? I thought it should last for at least a year? What should I do.

 

[clp]

After calibration does the probe read 7.0 and 10.0 in the appropriate solutions? Only use single use pH calibration packets for calibration as the bottled reference solutions are often quite inaccurate.

Curt

 

[Infinitereef]

yes, it does read 7 and 10 after calibration.

 

[clp]

Assuming the probe has been calibrated, I would have much more faith in the pH probe reading than any color matching test kit.
The color matching test kits are quite inaccurate, and will give different results depending on what type of light they are read under. Many test kits have their pH readings skewed to read a few tenths higher then reality. They do this because most tank's pH is below the 'desired' 8.3 reading, and if the user gets the pH reading they want to see they are more likely to buy their test kit again.

Curt

 

[raynist]

I have had a problem with mine as well. I bought the lab grade probe about 6 months ago. I recently recalibrated it with the 7&10 solution and now the probe is reading 0.5 below. I checked the water with another probe I have from another tank and the reading is fine.

How long should they last?

--Ray

 

[gweezpie]

I'll Jump in here for Curt since I got this answer from him. The probes should be good for 18 -24 months.