All about pH meters


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Jul 8, 2016
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Okay, from couple of grows in soil I've moved into Autopots and coco. So I bought Millwakuee pH meter with storage solution and pH calibration solutions. I am using AN nutes with pH perfect technology, but I found that pH is too high for coco (6.8) so I adjust it with pH- solution. I will track solution couple of days to see what is going on in reservior.

Question is:
- how often do I need to do calibration? Everytime before testing pH? I know this is best practicce, but it's also not so cheap.

- how often do I need to change storage solution (KCL)? I just sip it into pH meter cap, no sponge. Of course pH meter is standing in vertical position.

Any other recommendations? Maybe master @Waira has some tricks?
My way might not be the right way but my probes are always spot on when it comes time for calibration. I clean my probes and calibrate them every month.

The probe is usually wet when I put the cap back on so the cap never really dries out. Once a week I pour out the nacl and add fresh that's not mixed with water. I'm sure a can of compressed air would dry the probe enough so it wouldnt contaminate the cap. Then again I know a bunch of commercial guys who leave their ph and ppm probes in their reservious 24/7. The blue lab guardian has an alarm that goes off when things aren't within the set numbers so this basically means it's made to be left in the res.
:smoking: dewds..... Konop', what model is it? there's no sponge in the cap base? ...odd,... Yes, some lab-grade (non-portable) units have the electrodes immersed/stored in a calibration solution between uses,... others can sit in the res' as Sm0 says, but they need cleaning and calibrating frequently as well,.. deposits, residues can accumulate,...
...What water are you using with the AN nutes? With a 6.8 pH, sounds like it's tap, meaning it has hardness to it,.. RO/DI water should see the solution below 6.5 at least, from the AN videos I've seen,... yes they can "self-buffer" in solution ONLY, but any source of carbonate buffering will tax this ability,... and once in the pot, all bets are off because of what the roots themselves and the microbes do to affect pH, along with all the other chemical to chemical interactions with each other and the coco,... even the nute sitting in a res', aerated will see some drift from the CO2 getting dissolved into the solution forming carbonic acid, however weak and minimal,.. RO/Di has no buffering capacity because there's no CaCO3 in there (carbonate is what's involved with buffering),...
... pH meters are sensitive instruments, and must be treated so,.. rinse with RO/Di before and after every use; always use the storage solution (yup, KCl, not NaCl)... good care means you don't have to calibrate before each use,.. I keep part of the solutions (7.0, 4.0) in smaller containers for reuse, stored in the fridge,... I don't use mine much, but they get calibrated monthly at least; frequent use needs 1-2x/week,...
Thank you guys, some nice tricks from @BigSm0. I clean my probe with tap water rinsed on probe, then put cap on. I've read you are not allowed to clean it with hands or towel?

@Waira it's model 55. Just a normal pH meter, nothing fancy. Yes, I use tap water, which is pretty hard - 0.5 EC. But if I use rain water which is 0.0001 EC, then in 2 days I get some brown flakes on the surface when I mix nutes. You can see them here. If I let rain water sit in bucket for one week, this don't happen, so I guess it's something with nutes.
... clean with RO/di water only, tap has too much stuff in it,...
Huh! weird,.. yeah, 0.5 EC = 250ppm (American scale?).... that res' scuzz is a mystery to me, but I'm not a hydro guy, so maybe another person can call that,.... that it goes away if you let it sit is also weird,.. ..Collected how, what's it running over before collected? It looks like maybe biological contamination, unless the rain water is fouled with air pollutants-? Konop' I very highly recommend getting your own little RO unit, or get water from one of the self-fill machines at the stores,... tap is bad with the AN (they don't recommend it), and that rainwater is clearly compromised somehow,....
Tested rain water also with AN nutes. As I said, flakes on top of water. pH after 2 days is 7.0. First day was 6.1.
EC dropped from 2.25 to 2.2, but I don't think this caused pH to go up.

This of course didn't make troubles in previous soil grows, but now I am in coco and don't want 7.0 water in my reservoir. AN claims anything between 5-8 will be okay because nutes has chelates.. but NPK and non-chelated minerals in nutes will not be absorbed at my pH, I guess. Don't want to test, better stay safe.

Yea, I am looking for some cheap system in another thread, I don't want spend 100€ on RO system because I need only 20-30L of water per week for 2 plants.
I calibrate most weeks and replace the pen after a few grows but even that is beyond the design life of the device.

This vid is long but I found it informative....