pH Probes

jameson_uk

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In the spare time I don't have I have been thinking about whether I could hook up a raspberry pi to record pH and temperature. Temperature seems relatively trivial and I presume as accurate as most thermometers but pH seems a little bit more involved.

The bits to connect the probe to and handle input looks ok but I am struggling with probes....

I came across https://www.amazon.co.uk/dp/B00MGDWZ9I but it seems considerably cheaper than others I have seen so makes me think it would be useless?

I know probes are meant to be kept in a solution when not in use but would leaving it in the tank be ok? Does this type of probe have consumables that need replacing or could this just work forever?
 

zozo

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Lifespan depends very much on the solution the probe constantly is in. I guess the more agressive this solution is the shorter the lifespan. For example the horticulture industry is one the main industries that uses permanent PH and EC measuring equipment in their fert solutions. These solutions are relative to aqaurium water very agressive. Much higher in EC thus a rather high salt content and depending on the crop grown can go down to PH 5. For probes used in these conditions it needs a lot more regular cleaning and at one point the semipermeable membrane from the probe will wear off and or clogg making the probe inacurate.

In relative weak solutions as in life sustaining aqaurium water such a probe is much more long lasting. :) How long i can't tell you.. I only can tell you that i still have an over 20 year old Hanna Grow check permanent PH controller with the first probe and it still works the same as the day i bought it.

I guess the manufacturer gives worst case scenario advice on durabilty and takes the rest of it's customers with this advice as a huge profit along the way.
Simply because they can not give a valid data for any kind of scenario a Ph probe can be used.

Take for example a pocket pH meter, it contains the very same probe, but its a device not intended to use permantly. Thus it also suffers much less in use.
Have you ever read a data sheet that advices to buy a new pocket meter once a year? I didn't It says absolutely nothing about it and you can use them as long as they still work and give an accurate reading.

My personal conclusion is: As long as the permanent probe does its job as it should do, than why change a winning team? It not that they have a secretly build in time bomb that explodes after a year. As long as it works it works, what more can it do. That is what regular / weekly calibration is for. Tha you'll notice soon enough if it's off or not.

I've have been using a cheap $ 7 china probe from ebay for over 3 years permanently.. And i can only say i never experienced one reason to advice against them for hobby use as in aqaurium water. This simply aint agressive enough to wear 'm out within a year time. :)
 
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You will also need a amplifier to bring the voltage up to 5v /3.3v depending on what your rasberry pi needs.

I was using a arduino to take 1000 readings over 1 min then average the output the value and send it to my laptop.

Even measuring various solutions that I assumed should be stable I had horrible unpredictable outputs.

I bought two different pH sensors and still didn't manage to record anything that I believed in. I Never got to the bottom of it.
I believe measuring the pH close to 7 isn't as easy as it sounds.

Let me know how you get on.
 

dw1305

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Hi all,
I've have been using a cheap $ 7 china probe from ebay for over 3 years permanently.
I don't know quite how the cheap probes work, they won't have a silver (Ag) wire in the probe, but presumably a cheaper alternative metal.
Even measuring various solutions that I assumed should be stable I had horrible unpredictable outputs.
They are <"quite complicated bits of kit.">

I don't usually recommend putting too much reliance on pH as a measurement, that isn't because it isn't useful, it is just because of the technical difficulties involved with getting an accurate value, and the fact that the value might need some interpretation..

I believe measuring the pH close to 7 isn't as easy as it sounds.
You tend to get more uncertainty around pH7, it is because of the <"log10 nature of pH as a scale">. The simple answer is that small changes in water chemistry cause large changes in pH around pH7. If you move into the acids, at pH6 you have a ratio of 10:1 of H+:OH-, at pH5 100:1 etc. This is the titration curve for a strong acid/strong base, pH7 is the "equivalence point", where you have a ratio of 1:1 for OH- and H+ ions.

That is why they use a neutral salt (3M potassium chloride (KCl)) as the reference solution, it has lots of ions (the three molar bit) and a ratio of 1:1, so it is always pH7.

sasb1.gif


You also have more difficulty in getting a stable result as conductivity falls, this is because the meters work via <"ion exchange">, and measures a voltage (potential difference). In solutions without many ions that takes a long time.

cheers Darrel
 

zozo

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I don't know quite how the cheap probes work, they won't have a silver (Ag) wire in the probe, but presumably a cheaper alternative metal.
I don't know either, they look the same and always do calibrate correctly at 4 and 7 solution. Than i can only assume they are relatively accurate. I gave it a try because there was little to lose at that price vs an original Milwaukee or Hanna probe. The nice thing is also comes with a refill kit while the originals are sealed shut.

But as you say getting stable or reliable results is pretty impossible, i have used quite some different Ph meters over the years pocket version and probe versions. Remarkable is i've used 4 different meters all calibrated correctly but still deviated 0.# in value bellow and over pH 7 no 2 giving the same result. Also here i can only asumme it might be the solution in the probe was differnet value cuasing it. Or maybe electronic treshhold accuracy difference. Its a what you see is what you get scenario and make a pick. But since i stoped using CO² i actualy do not care anymore about pH i have no reason to care much for it.

Than quite a few should not be put in the tank with other electrical devices switched on, this can have drastic false readings. Sometimes stable but wrong with others shooting up and down like mad. Why some meters are so darn sensitive to it and others less or not is a complete mystery to me.
 

dw1305

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Hi all,
neutral salt (3M potassium chloride (KCl)) as the reference solution
That should have been three molar KCl for the storage solution and 0.1M KCl for the reference solution (insider the probe).
The nice thing is also comes with a refill kit while the originals are sealed shut.
They all used to be refillable (with KCl), most of the newer probes are sealed, and have a finite life.
I don't know either, they look the same and always do calibrate correctly at 4 and 7 solution.
Usually you can buffer the meters, the buffer solutions have stable pH and are pretty "salty".
But as you say getting stable or reliable results is pretty impossible,
I use the bench meters at work for making up buffer solutions etc., but they are over £thousand for each meter. As well as the wire (silver chloride (AgCl) coated silver wire) the glass membranes of the pH probes are made of a special glass, which makes me wonder how cheap the electrodes can be and still work accurately.

I very rarely dip the portable pH probes in the tanks, they are all heavily planted and have low conductivity (less than 150 microS) water. The pH reading really just measures how <"much oxygen is in the water">. We often have the <"stable pH"> conversation on other forums, and it rarely goes well.
Than quite a few should not be put in the tank with other electrical devices switched on, this can have drastic false readings
Yes, you need to turn off all the electrical kit of when you take pH and conductivity readings.

cheers Darrel
 

Zeus.

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Than quite a few should not be put in the tank with other electrical devices switched on, this can have drastic false readings. Sometimes stable but wrong with others shooting up and down like mad. Why some meters are so darn sensitive to it and others less or not is a complete mystery to me
Yes, you need to turn off all the electrical kit of when you take pH and conductivity readings.
So 'in theroy' a pH controller should only be used in a tank with no filter or lights which are powered by electric :eek: Best get my mirrors out and sort some mechanical pump out at attaches to my bike and get pedalling ;):lol:

But joking apart, my pH probe on the pH controller does give a different reading when my T5 come on, it not massive but its there
 

zozo

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So 'in theroy' a pH controller should only be used in a tank with no filter or lights which are powered by electric
Yes.. :) But it highly depends on the meter used.. The ones that use a ground penn in combination with the probe to reference are in my experience absolute stable.
Hanna GroCheck has such a ground penn, but this again is absolutely a horticultural meter and uses a rather high current, it sends from penn to probe. At least i could feel te current in the water sticking a finger in it with the Ph meter in it as well. The voltage was low but current high enough to cause sensation, like rising hairs on my arm.

Gro Check with ground penn..
hanna-gro-check-combo-4836-nl-G.jpg



I would say no good for use in fish tanks.

Compared to my Milwaukee that has no seperate ground penn for reference has a much lower current. The ground is likely in the probe too.. And is rather very susceptible to interferance. What comes from balasts and or pumps or even led fixtures into the water over the atmosphere or direct contact from insulated devices is i believe Capacitive Current and not as often stated inductive current. Never the less if grounded it can be measured as voltage. The Ph probe needs a ground to reference the voltage difference it measures. Thus when the probe is put in the water this capacitive current will exit over the pH meter to the ground and can influence the reading.

Capacitive current in the aqaurium is something common and probably inevitable as long as electrical devices in and around it are used.

I once had a flaming discussion about it with an so called electrical ingeneer... He stated permanently it is harmless as long as there is no ground.. But my argument was the question. If a Tube light balast or led fixture only needs the atmosphere without ground to blast current into the water column, than what is the argument that it absolutely can not exit via the very same atmosphere. Does electrical power absolutely need ground to flow? Can Atmosphere provide ground enough? We simply can't know because we are not able to measure that without a physical ground connection. He called me an idiot, because he was electrical ingeneer and i'm not. But explanations yet never came.. :rolleyes: I believe there is a lot to electrical power we yet still do not know.. But anyway thats something completely different.. :)
 
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Zeus.

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I once had a flaming discussion about it with an so called electrical ingeneer... He stated permanently it is harmless as long as there is no ground.. But my argument was the question. If a Tube light balast or led fixture only needs the atmosphere without ground to blast current into the water column, than what is the argument that it absolutely can not exit via the very same atmosphere. Does electrical power absolutely need ground to flow? Can Atmosphere provide ground enough? We simply can't know because we are not able to measure that without a physical ground connection. He called me an idiot
Think he was the idiot m8. For electric to flow all you need is the ability for electrons to move, which happens in the atmosphere all the time :rolleyes: it may only be a very small amount at time but its there all the same. If I had a very very very very small amount of a nations turnover I would be a very very very very wealthy person :lol:
 
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