Two PH pens, calibrate fine, but give different readings

[Custom45]

Hi,
So I currently have 2 ph pens/meters, both decent quality. They both calibrate well in 7 solution and read 7 just fine. But when dipped in tap water or nutrient solution there's a big difference in reading between the two (one reads 5.8 the other 6.5). I can't understand why they read the 7 solution just fine, but then get wildly different readings in anything else.

I don't know which one is correct or which one to trust?!

 

[freezeland2]

Hi,
So I currently have 2 ph pens/meters, both decent quality. They both calibrate well in 7 solution and read 7 just fine. But when dipped in tap water or nutrient solution there's a big difference in reading between the two (one reads 5.8 the other 6.5). I can't understand why they read the 7 solution just fine, but then get wildly different readings in anything else.

I don't know which one is correct or which one to trust?!

Are the probes clean and how old is your calibration solution? Do you have cal 4 solution? Typically you calibrate both.

 

[Custom45]

Are the probes clean and how old is your calibration solution? Do you have cal 4 solution? Typically you calibrate both.

Probes are clean, yes. Solution is about 1 year old, just have the 7. I'm ordering some more and will get a 4 and 7. I'll get some of the storage solution too.

I just find it odd that they both read fine in the calibration solution, but read different in anything else.

 

[Moshmen]

Drops from a fish place are more reliable than a cheap pen, now you want to spend 100+ there’s some nice stuff that still needs maintenance drops have worked for me for like 5$ for a years worth

 

[freezeland2]

Probes are clean, yes. Solution is about 1 year old, just have the 7. I'm ordering some more and will get a 4 and 7. I'll get some of the storage solution too.

I just find it odd that they both read fine in the calibration solution, but read different in anything else.

You haven’t finished the calibration process with only one cal standard. The stuff also starts going bad after 3 months.

 

[josefrahl]

Yeah, if you don't calibrate 7 & 4 it's not actually calibrated. They won't know the gradual differences. So say in your case one thinks the grade difference is .25 and one thinks its .6. (Just to make the math easy). When calibrated they should recognize the difference at .1.

 

[Zill]

A man with two watches never knows what time it is.

 

[Zen_Seeker]

A man with two watches never knows what time it is.

Sorry, can’t agree. More than once I’ve worked at a place that supported users around the world. We had 3 or 4 clocks on the wall for each time zone.

However confucious said; “Man who gets laid on grass has peace on earth.”

 

[Moe.Red]

Depending on what you paid for them, keeping the tips wet may be a requirement. If they have a screw on or some way to hold a little cup on the tip, that is a pretty good indication.

Cheap $10 pens not so much. More expensive like bluelab, yes you cannot let them dry out. Doing so may damage the sensor.

But yes minimum 2 point calibration (3 is better, 7, 4, 10) or you will only be able to track if something is or is not 7.0PH.

 

[GreenGalaxyFarm]

If they have a screw on or some way to hold a little cup on the tip, that is a pretty good indication.

your asking whether his ph pen has a cap for storage solution?

 

[Moe.Red]

your asking whether his ph pen has a cap for storage solution?

Saying that if it does it is an indication it is supposed to be kept wet.

If OP lists the specifics of the equipment I could be sure. There is more than 1 PH probe style, and the more expensive ones are more accurate but require care.

 

[Custom45]

Drops from a fish place are more reliable than a cheap pen, now you want to spend 100+ there’s some nice stuff that still needs maintenance drops have worked for me for like 5$ for a years wort

The pens were £75 and £55, so not cheapy china pens. Not been using storage solution, however I have ordered some, along with 4 and 7 solution for proper calibration. Both have caps with space for storage solution.

When it all arrives I'll calibrate them and see what happens. My tap water is usually 7.3/7.4ph, so I'll see what both read.

 

[Custom45]

Saying that if it does it is an indication it is supposed to be kept wet.

If OP lists the specifics of the equipment I could be sure. There is more than 1 PH probe style, and the more expensive ones are more accurate but require care.

Sorry, one is a Bluelab pen, other is an Apera ph20 pen. I think both should be stored wet in solution, but I only recently found that out and haven't been doing so.

Thanks for all the replies. Hopefully I haven't buggered these two up, if I have I'll get another and make sure it's kept properly.

EC pens, should they be stored the same?

 

[Moe.Red]

Sorry, one is a Bluelab pen, other is an Apera ph20 pen. I think both should be stored wet in solution, but I only recently found that out and haven't been doing so.

Get it in storage solution (KCL) and let it sit for a few days before you calibrate. It may reset itself. Let us know your results.