Have I bought a duff pH probe?

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guypettigrew
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Have I bought a duff pH probe?

Post by guypettigrew » Thu Nov 14, 2019 12:44 pm

About a year ago I bought one of these as a spare in case the probe which came with the Voltcraft PH-100ATC meter needed replacing. The probe has just stayed in its packaging in a drawer since then.

Today I thought it was time to unpack it and try calibrating it.

The readings are totally unstable. Calibrated at pH 7.00, the reading drops over 10 minutes or so to 6.8 or below. Recalibrating it to 7.00 and the read out drops again, and again, and again! In the pH 4.0 buffer the reading goes up, and up....

Putting the probe back in the pH 7.0 buffer it reads high, 7.35. After recalibrating to 7.0 the reading drops again, and again!

The probe is rinsed in RO water between readings and wick dried. It's left in the buffers for 5 minutes or so to allow the reading to stabilise (ha ha!)

Should I have splashed out on a proper Voltcraft probe?

Guy

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orlando
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Re: Have I bought a duff pH probe?

Post by orlando » Thu Nov 14, 2019 1:44 pm

Bad luck. Was it stored in storage fluid specific to pH probes? Apologies for the obvious but have you tried the probe with new a battery? My Voltcraft does exactly that once the battery begins to die.
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Re: Have I bought a duff pH probe?

Post by guypettigrew » Thu Nov 14, 2019 3:06 pm

It's been in the proper fluid since it arrived. Battery? Hadn't even crossed my mind. I'll go and check the one in the Voltcraft now. Thanks for the idea.

Guy

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Re: Have I bought a duff pH probe?

Post by guypettigrew » Thu Nov 14, 2019 3:12 pm

The battery's still good. Shame, would have been an easy fix!

Guy

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Re: Have I bought a duff pH probe?

Post by orlando » Thu Nov 14, 2019 4:36 pm

Pity. Well the replacement I bought was this one. Have to say it's been brilliant and at that price you can't go wrong.
I am "The Little Red Brooster"

Fermenting: No Stout About It (Porter)
Conditioning: 4 Hops To Heaven
Drinking: From Russia With Love (RIS), Peaches, Twist & Stout, I Am A Patriot Too, Reasons To Be Beerful (Part Three)

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Planning: Winter drinking Beer

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Re: Have I bought a duff pH probe?

Post by guypettigrew » Thu Nov 14, 2019 4:56 pm

Thanks Orlando. Ordered. The other one is going in the bin.

Guy

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Re: Have I bought a duff pH probe?

Post by orlando » Thu Nov 14, 2019 5:00 pm

50p more than I paid :evil: Thieving swines.

Be interested in your review.
I am "The Little Red Brooster"

Fermenting: No Stout About It (Porter)
Conditioning: 4 Hops To Heaven
Drinking: From Russia With Love (RIS), Peaches, Twist & Stout, I Am A Patriot Too, Reasons To Be Beerful (Part Three)

Up Next: With A Bitter Luck, Song For Keith
Planning: Winter drinking Beer

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Re: Have I bought a duff pH probe?

Post by PeeBee » Thu Nov 14, 2019 5:09 pm

Twelve months is often quoted as the useable life of a pH probe, although deteriorating as bad as you are experiencing seems a bit off.

But the really important bit: The probes deteriorate about as quick unused as used. Bummer that isn't it! Stockpiling "spares" is a real no-no!

My own probe is becoming very difficult to calibrate - classic sign of "wearing out" - and is only about six month old. Damn!

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Re: Have I bought a duff pH probe?

Post by Eric » Thu Nov 14, 2019 5:43 pm

The original probe for the same type of meter didn't last a year. My replacement was the same as Orlando's, I can't remember when, but it was several years since and it calibrates perfectly in seconds. Doubt I'll be as lucky next time.
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Re: Have I bought a duff pH probe?

Post by guypettigrew » Thu Nov 14, 2019 6:03 pm

PeeBee wrote:
Thu Nov 14, 2019 5:09 pm
The probes deteriorate about as quick unused as used. Bummer that isn't it! Stockpiling "spares" is a real no-no!
What is it that deteriorates? Isn't the solution they are kept in supposed to keep them working OK?

Guy

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Re: Have I bought a duff pH probe?

Post by Jocky » Thu Nov 14, 2019 7:27 pm

That probe has a little hole in a blue collar around the top, and comes with a syringe.

Why?

My original voltcraft probe didn't have either. I can only guess it's to fill the probe with some kind of solution.
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Re: Have I bought a duff pH probe?

Post by PeeBee » Thu Nov 14, 2019 7:31 pm

guypettigrew wrote:
Thu Nov 14, 2019 6:03 pm
What is it that deteriorates? Isn't the solution they are kept in supposed to keep them working OK?
Ah, don't remember of top of me 'ead (not even sure I put the top of me 'ead back after checking it last time). Nor do I have links handy, but they're out there if you do a bit o'Googling.

But from what I remember the probe exchanges charged ions about the place (through the "electrolyte" in that glass bead) a bit like a battery. And like a battery it goes "flat" after a while. The "storage solution" slows this down (don't stop it and doesn't reverse it). If you don't read the instructions and keep the probe in deionise/distilled water, the process speeds up.

There, you've now got as much dodgy knowledge about it as me and can spout the same level of possible claptrap as I do. Unless you work at it and find the real reason, in which case, can you tell me?

guypettigrew
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Re: Have I bought a duff pH probe?

Post by guypettigrew » Thu Nov 14, 2019 7:46 pm

Thanks for the info peeb

Cracked it now, bearing in mind your helpful info.

the ions have clearly all fallen out in my cheap ebay probe. Should never have left it in the upright position. In fact, I've just looked at the little bottle the probe is stored in, and it's absolutely stuffed full of ions. Explains everything.

Guy

Ps hope you find the top of your head, unless it's full of rubbish, in which case, better off without it.

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Re: Have I bought a duff pH probe?

Post by Eric » Thu Nov 14, 2019 8:23 pm

Jocky wrote:
Thu Nov 14, 2019 7:27 pm
That probe has a little hole in a blue collar around the top, and comes with a syringe.

Why?

My original voltcraft probe didn't have either. I can only guess it's to fill the probe with some kind of solution.
No, my original didn't either, possible the reason for its early demise.

The hole has 2 functions. First as you advised, to top up the potassium chloride solution (also used as storage solution) and secondly to be open when in use to ensure the fluid inside contacts with the junction.
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Re: Have I bought a duff pH probe?

Post by Jocky » Thu Nov 14, 2019 10:24 pm

Eric wrote:
Thu Nov 14, 2019 8:23 pm
Jocky wrote:
Thu Nov 14, 2019 7:27 pm
That probe has a little hole in a blue collar around the top, and comes with a syringe.

Why?

My original voltcraft probe didn't have either. I can only guess it's to fill the probe with some kind of solution.
No, my original didn't either, possible the reason for its early demise.

The hole has 2 functions. First as you advised, to top up the potassium chloride solution (also used as storage solution) and secondly to be open when in use to ensure the fluid inside contacts with the junction.
Thanks Eric. My original lasted several years thanks to careful cleaning and storage and just started to wander a bit. Cheap Chinese probe ordered.

Gobsmacked how much the price of the voltcraft meter has gone up since I got mine, it must be over double price since 2015.
Ingredients: Water, Barley, Hops, Yeast, Seaweed, Blood, Sweat, The swim bladder of a sturgeon, My enemies tears, Scenes of mild peril, An otter's handbag and Riboflavin.

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