PH pens making me nuts

[RaggedyMan]

I had a cheap tester that would calibrate good but when I tested it against a newer pen (Oakton ecoTster) in the reservoir it was off. I just today got another pen as a backup (Apera ph60). I calibrated both of them at 7.0 but in the reservoir one registered 5.9 the other 6.5. Both of these pens are 70-$80 units so it's not like I bought the cheapest ones I could find. How the hell does a person know what to go by? Several years ago I resorted to an aquarium test kit only to find that the cheap pen I had was way off, maybe that's the way to go

 

[Chris Scorpio]

White vinegar is a pH of 2.4... when I'm in doubt, I'll check them against it

Plus... Test goop of 4 and 7 calibration is better than just one

 

[Virgin Ground]

Yeah. Need to calibrate to at least two points. 4 and 7 like Chris mentioned. Try again after this step. Make sure you are storing them correctly as well. Don't store them in distilled water. The Apera uses a 3m kcl storage solution. I'm sure the Oakton requires something similar. Different probes can use slightly different storage solutions so make sure your tester is compatible.

 

[Big juice]

get yourself a blue labs ph/conductivity pen you'll thank yourself later imo.

 

[TurboBucket]

I have a pH60. Been using it for 3 years now. I've calibrated it a couple of times to double-check but it's never needed it. The thing has always been rock solid. Full disclosure: I abuse the thing, it was only stored in solution for the first couple weeks I had it. Since then I dry it off and hang it up by the lanyard. Still going strong but I'm planning for it to fail soon, 3 years is a good run. I'll definitely buy another apera but probably the 80 with replaceable probes.

One thing to consider on the varied readings. Sometimes the ATC (automatic temperature correction) is slow. If there's a big temperature difference between your probe temp and the water temp sometimes it takes several seconds for the reading to correct. Maybe 7-15 seconds, slightly annoying but not the end of the world. Just a thought.

 

[RaggedyMan]

I dug deeper thanks to y'all's replies and found the Oakton pen was older than I thought. I calibrated it at 7 then at 4. Once done I rechecked it at 7 again and it was way off, the new pen worked perfectly.

Do you guys store your pen in solution all the time or just when it's going to sit unused for a while? I check the pH and TDS normally twice a day, sometimes more. I keep the cap on them in between but haven't been keeping either in solution.

 

[Virgin Ground]

I use an Apera pH90. This has a slightly different probe that will not be ruined if it is left to dry. Not sure if its the same probe That the pH60 has. It should tell you in the manual.That being said, I operate on an ultra tight budget so I make it a point to take care of my equipment. I store mine in the cap with it's storage solution. It only takes a few extra seconds to protect your investment.
I wouldn't leave the Oakton to dry. I think they have a probe that has to remain hydrated.

 

[SmokeLake]

I have had this same issue to the point that I took my ph pen back to the hydro shop and proved that his pen was off as well. I walked out with a free replacement and I purchased a new spare for myself. The gist is I found that no storage solution was better than simply rinsing in clean water then drying the majority of the moisture and caping the probe. The meter will last a few years and be effectively worn out. This seems normal honestly not sure how frequent or infrequent use effects the time it last for. The temp compensation does take more time and ph pen I find needs a couple minutes to fully stabilize and read accurately simple dip and read I find doesn’t work as well. My pen will drop as I add ph down to get to 6.1 say but if i put it back in tap water it will always read below the 7.5 it read in tap water before being in nute solution why is this? And so here in lies my debate once the probe absobes and reads a solution a certain amount must be trapped and then diluted in the next solution to be read in order to read accurately and this is why theres a delay in stability.
i hope this makes sense im pretty high.
happy420!!

 

[nivek]

just my two bits here,, for those of us on a tight budget,,

i use the generic yellow $20 amateurlike ph pen. and i am on my second one.. ha

if one has to buy the calibration solution, but can or only wants to buy one of the solutions,, ph7 or ph4,, my logic tells me to buy the ph7 calibration solution since most of the ph measuring i do is in the 'ph6' range,, the ph7 solution is perty darn close to this,, so should give a fairly reliable ph 6 reading if calibrated often

which i do

now,, if @Chris Scorpio is correct, and white vinegar ph's at 2.4 as stated,, well, there is another calibration point that can be used

bonus,, cheers

 

[TLC]

I gave up on ph pens and decided to stick with the old fashioned method..

 

[ColonelBlake]

The Apera ph60 has been rock solid for me. I calibrate it every few months using the supplied solutions. It's always very close to the test solutions. I do store mine in kcl solution.

 

[BooMtoLate]

I have 4 ph pens and everyone gives a different reading. It’s good times

 

[PurpleSpace]

I got 3 and I’m fortunate enough that 2 read the same.. will be investing in a blue guardian or apera wall mount meter.

 

[iNeedMeds]

I just use tear off test strips. They are accurate enough for hydroponics, cheap, never break, don't need calibration, no special storage procedures, and no dead batteries. Where electronic pH measurements matter, is when you want automated pumps to limit pH drift. The only meter you really need, is an EC meter.

However, if you love tech, bluelab makes a nice pH pen.