meter me thinks.. Lol
I leave the ph probe in the res and it drifts off a little bitty bit every month, maybe from air stones or 9v battery vs power plug. No idea but they do drift off eventually !
I went to school for water treatment engineering and pH probe calibration and maintenance was drilled into us.
The meter works by an ion exchange through the glass tip. There's a tiny ceramic embedded in the glass that allows ions to flow in and out of the probe. The glass is full of KCl solution and each time that it's immersed in solution, some of that KCL is lost through diffusion - at the same time osmosis pulls water into the probe. This change in KCl since the last calibration is what causes drift. Using the KCl storage solution will recondition the probe by "recharging" the inside of the glass.
Never leave a probe in RO or DI water for a long period of time - it will strip out the KCl completely, probably rendering the meter useless. There are a handful of practices that will keep your probe lasting a very long time.
There's also good technique to getting a consistently accurate calibration. Your meter will only be as accurate as your technique. If you contaminate your standard solutions, then your calibration will be off - even though it completes the calibration. You're telling it what 4 and 7 pH look like - if your 4 and 7 solutions are no longer 4.0 and 7.0 - then you're mis-calibrating the meter.
Always rinse your probe and sample container with the solution to be tested, discard - then fill the sample container and take a reading. You're rinsing off things that might skew your pH. Like - if you take your probe out of 7.0 solution and dip it into the 4 - well, now the 4 is no longer really 4... Also, never pour solution back into the bottle. Once it has left the container, consider it contaminated.
Always do a 2 point calibration with both 4 and 7 - then it will be accurate between those points. The further away from 4 or 7 that your reading is, the less and less accurate it becomes. If you only calibrated with 1 solution then it would literally only be accurate at that single point.
It's a good idea to do all of these things - AND recalibrate at least monthly. New bottles of standard solutions are a whole lot cheaper than sick plants.
mentions RO water
