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On 6/21/2021 at 3:27 PM, Jarred said:

Hey everyone,

I am working on a project that uses a ph probe. I know they need to be calibrated once and a while, but is it true the probe needs to be replaced often?

The calibration process is usually a reference test against at least 2 (sometimes more) sample standards of pH level.  When the unit proves "un-calibrateable" to these multiple standards, the probe must be replaced.  In a freshwater aquarium environment, this will certainly not happen often (maybe never), but is more the case with frequent testing of caustic or harsh substances.

Edited by tonyjuliano
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On 6/21/2021 at 3:52 PM, tonyjuliano said:

The calibration process is usually a reference test against at least 2 (sometimes more) sample standards of pH level.  When the unit proves "un-calibrateable" to these multiple standards, the probe must be replaced.  In a freshwater aquarium environment, this will certainly not happen often (maybe never), but is more the case with frequent testing of caustic or harsh substances.

YEAH…what he said…😂
 

He worded it perfectly.  I have had mine for years and it is still working perfectly.

Edited by ARMYVET
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A lot depends on how they're being used and /stored/.  It seems like black magic to me but there's something about how the glass is doped and prolonged exposure to pure water or certain ions can deplete or exchange ions in the glass and damage your probe.  Generally it's recommended to store the glass electrodes in 2-4M KCl when not in use. 

 

I've seen manufacturers recommend replacing every 1-2 years but I think it also comes down to the accuracy you need.  I think that's the recommendation to ensure they're in spec (sometimes as good as 0.001ph).  In practice I think you just replace them whenever they don't work as well as you'd like or don't hold calibration.  for fish +/- 0.2 is fine and within 0.1 would be outstanding, so there's a lot of wiggle room.

 

The same goes for calibration period.  I've read daily or more and up to monthly or less depending on conditions and what you need.

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