Calibrate ph probe, how often?

[dartfrog]

I have had an Apex Lite for about 3 months, and have calibrated the ph probe twice now, both times it was off by about .2 on the low side. Both times I thought it was the water, but figured it out before making any adjustments. It seems low again today, I will double check it when I get home today, but I'm thinking it is the probe again, and not the water...how often do y'all have to calibrate your probes and how much is yours out of wack when you do it? Is this normal, about monthly?

Thanks

 

[acroholic]

Technically, you are not calibrating the probe, you are calibrating the controller to the probe. I do mine every 3 months or so. Probe replacement about every year-15 months. The probes wear out over time.

 

[dartfrog]

Whan you do calibrate it, how much is it off by if any? Do you calibrate it because you notice somethings off or is it just part of your routine?