# Looking after PH Probes, how ?



## tubamanandy (25 Feb 2014)

Anyone know how you are supposed to look after PH probes for longevity ?

Years ago, you were supposed to keep the PH Pen type probes in some sort of solution but not sure these days.


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## dw1305 (25 Feb 2014)

Hi all,
Assuming it isn't a solid state IFSET probe?, You need to store the electrode in a 3M KCl storage solution. Once the membrane has dried out it will never give reliable readings. 

You can buy the solution, but it is much cheaper to make your own "_dissolve 22.4g of KCl into 100cm3 of DI water_".

Details are here: <pH maintenance>.

cheers Darrel


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## tubamanandy (25 Feb 2014)

Thanks Darrel


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## dw1305 (26 Mar 2019)

Hi all, 





dw1305 said:


> You can buy the solution, but it is much cheaper to make your own "_dissolve 22.4g of KCl into 100cm3 of DI water_".


I should have put the workings for that. 

potassium (K) RAM = 39.1 
chlorine (Cl) RAM = 35.5

potassium chloride (KCl) RMM = 39.1 + 35.5 = 74.6 

So 74.6g of KCl made up to 1 litre with DI water is a molar solution. 74.6  multiplied by 3 gives you 224g, and 224g of KCl (in one litre of DI) water is a 3 mol. solution of KCl. 

Divide them both by 10 and that gives 22.4g of KCl in 100cm^3 of DI water is a 3 mol. solution.

cheers Darrel


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## Zeus. (26 Mar 2019)

dw1305 said:


> You need to store the electrode in a 3M KCl storage solution. Once the membrane has dried out it will never give reliable readings.



I have had the pH probe for my pH controller fitted on my tank for 15 months so not the ideal storage solution and its still OK. I assume that if the probe in stored in the correct solution it lasts longer ? 

Did try storing my Hanna pH pen in solution but it evaporated pretty quick in a beaker and when I put the solution in the lid/cap as it suggests its a real PITA to get the lid/cap off!


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## dw1305 (26 Mar 2019)

Hi all, 





Zeus. said:


> I assume that if the probe in stored in the correct solution it lasts longer ?


It does, the reference electrode used to be refillable with KCl, but now they are often sealed, so once the KCl has leaked out you have to buy a new electrode. 

cheers Darrel


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## Zeus. (26 Mar 2019)

dw1305 said:


> Hi all, It does, the reference electrode used to be refillable with KCl, but now they are often sealed, so once the KCl has leaked out you have to buy a new electrode.
> 
> cheers Darrel



Oh I see or think I do . The electrode has KCI in it, when its leaked out or diffused out its reference pH is not what it should be, by storing it in the correct solution 3M KCI it helps maintain the correct concentration of the KCI within the electrode as the KCI solution will also diffuse into the electrode by diffusion if it can, thus if they are both the same [KCI] there with be a neutral diffusion gradient.


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## dw1305 (26 Mar 2019)

Hi all,





Zeus. said:


> Oh I see or think I do . The electrode has KCI in it, when its leaked out or diffused out its reference pH is not what it should be, by storing it in the correct solution 3M KCI it helps maintain the correct concentration of the KCI within the electrode as the KCI solution will also diffuse into the electrode by diffusion if it can, thus if they are both the same [KCI] there with be a neutral diffusion gradient.


Yes, exactly that.

cheers Darrel


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## X3NiTH (26 Mar 2019)

I knackered one of my probes by swapping out the tank water to about 50:50 of my usual mix and RO/DI to TDS match the water to what Electric Blue Rams were coming from the store in, it was going fine and showing good accuracy after a year in KH8 GH8 and now it doesn't. Restoring in storage solution rejuvenates it but it can't hold onto the value and plummets when put back in the tank (which is now back to GH/KH8), it got a good running but now It needs replacing, not bad for a £7 electrode that stayed calibrated to a high degree of accuracy over a few months and even when it was out of calibration it was not by much, say around 0.3ish pH.


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## zozo (27 Mar 2019)

Few years ago i bought a set of these, couldn't resist getting curious for this price.
https://www.ebay.com/itm/Aquarium-H...m58cbb155c0:g:8OAAAOSwOztciKle&frcectupt=true

These are refillable and come with an extra refill in the package.. I've used it on a Hanna Growcheck and on a Milwaukee SMS pH meter. Off which i allso still have the original probes. Must say this performes excactly the same as the original electrodes which are not refillable. Quality and longevity also is ok, used one for over a year and it never did let me down.

In price comparance to the original ones, even if they would live only half the time an original one lives, you still save quite  a lot.

The only negative point is, the cable on the BNC connector is rather short. It depends if it needs an extension.


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## Oldguy (31 Mar 2019)

zozo said:


> BNC connector



The good thing about BNC connectors are that they are an international standard and you can just about buy any  type. ie female to female, male to female etc. A length of screened cable and a soldering iron job done. Best to match 50 ohm to 50 and 75 to 75. Takes me back a few years.


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## obsessed (31 Mar 2019)

if you buy a decent probe they last a couple of years you can store them in ph 4 test solution (air tight) mine are constantly wet which in turn with a monthly delicate scrum and a recalibration last in freshwater.. blue lab bnc probes are 1 of the best.. I've used allot over the years.. this is just my way..


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