# Cleaning a pH probe?



## Zapins (Jul 28, 2004)

Anyone know the correct way to clean a pH probe? I've had a Milwaukee pH probe sitting unused in one of my 10g tanks (underwater) for years and years now and it is tarnished now, probably by algae. I'd like to see if it still works (I've got calibration solutions I can use). But how do I clean it without damaging it?


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## Zapins (Jul 28, 2004)

Bump, where are the chemistry buffs?

*edit*

I found the info http://www.eutechinst.com/techtips/tech-tips26.htm

Cleaning

The solution used to clean pH electrode depends on the presence of possible contaminants. Mechanically intact electrodes may show slow response due to coating or clogging. Use the guide below to choose the appropriate cleaning solution options:-

For general cleaning: Soak the pH electrode in 0.1 M HCl or 0.1 M HNO3 for 20 minutes. Rinse well in tap water before use.​
For removing stubborn deposits and bacteria: Soak the pH electrode in a 1:10 dilution of household laundry bleach for 10 minutes. Rinse thoroughly before use.​
For removal of oil and grease: Rinse the pH electrode in mild detergent or methyl alcohol. Wash in water before use.​
For removal of protein deposits: Soak the pH electrode in 1% pepsin in 0.1m HCl (EC-DPC-BT) for 5 minutes. Rinse well in water before use.​


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## jrIL (Apr 23, 2005)

I am kinda surprised your just not replacing it if its that old.

Sent from my DROID RAZR HD using Tapatalk


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## Zapins (Jul 28, 2004)

It costs $60+ to replace and money is tight for me right now. If it still works after a cleaning then no need to replace it, if not, I don't really need it that badly and will box it up for another day.


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## neilshieh (Jun 24, 2010)

you should probably use one of those lint free paper wipe thingies too. That's what we did when using ph probes.


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## Yo-han (Oct 15, 2010)

I believe my lab guidebook stated something very similar to the cleaning procedures you found, so should work!


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## Zapins (Jul 28, 2004)

Good to know. I think I'll give it a good bleaching and then possibly rub it clean with a soft cloth. Maybe give it a second bleach dip to be sure.

The glass bulb at the tip of the meter looks intact so I don't see why it wouldn't work once cleaned. I plugged it in just now and it is reading 8.2 in the bag of water I stored it in to keep it wet. I haven't tried a different water source yet so I don't know if the probe will change readings before it is cleaned. In any event I've got the calibration fluids so I can test it out thoroughly later.

I really only need the pH probe for my CO2 deficiency experiments. I want to monitor the pH of the tank water as I scrub it of all CO2. This is because when there is no CO2 in a tank all the carbonates in the water convert into CO2 and degas which drastically raises the pH to 11 or so. I must make sure that the water remains around 6-7 during the test to keep the two tanks as similar as possible.


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## Tugg (Jul 28, 2013)

Wouldn't it crash instead of raise once the kH is consumed? I would suspect that as the CO2 is removed, it would climb to 8.3, then as the kH is removed, it I would be more like a South American tank with a pH around 5. Why would it go up above 8.3? What am I missing?


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## Zapins (Jul 28, 2004)

A very good question. This is my understanding of why the pH rises.

Equilibrium equation:
CO2 + H2O ↔ H2CO3 ↔ H1CO31- ↔ CO32-

Normally as you add CO2 to the water the equilibrium shifts to the right and you make carbonic acid (H2CO3), which decreases the pH as it dissociates. The opposite is true as well, when you remove CO2 from the water the equation shifts to the left and CO2 gas and water are produced.

Ordinarily this relationship maintains a fairly constant pH value because CO2 is exchanged between the air and the water maintaining a balance. However, in my experiment I will be continually removing CO2 gas from the tank and the air space above it by piping in CO2 free air. This will prevent the tank from coming to a normal equilibrium which allows some carbonates to remain in the water. What will happen instead is all the free H+ (acid) in the water will be used up as it produces more H2O and some of the carbonates (CO32-) will be turned into CO2 gas and flushed out of the system by the constant inflow of CO2 free gas. At some point all the free H+ ions in the water will be removed and the lack of free H+ ions will prevent anymore CO32- from being removed from the water. Since CO32- will be the dominant species in the water and it buffers at around pH 11.3 the pH of the tank will also be around this pH.









*Image From*:http://ion.chem.usu.edu/~sbialkow/Classes/3650/Carbonate/Carbonic Acid.html​
Since the conversion of carbonates to CO2 and H2O depends partly on free H+ ions in the water this means that the pH cannot be stably adjusted by simply adding acid to lower the pH into a normal planted tank range. An alternate method of maintaining a favorable pH must be used.

Using a buffer that does not use carbonates is the solution. Non-carbonate buffers do not participate in the CO2 + H2O ↔ H2CO3 ↔ H1CO31- ↔ CO32- equilibrium reaction, so no buffering capacity is lost to the atmosphere. These buffers can therefore maintain a stable pH under CO2 free conditions. For this reason a small amount of the widely available API 6.5 pH phosphate buffer will be used to maintain a favorable pH in the test tank.


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## Tugg (Jul 28, 2013)

This looks like a great read in relation to your pending experiments.
http://www.jstor.org/stable/2258685

From my laymen read of the extract, it seems to parallel what you want to do, but at a full lake level.

I really look forward to this future thread.


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## Zapins (Jul 28, 2004)

1st- Tugg that is an awesome paper! I've had a hell of a time finding carbon deficient papers on plants or algae for that matter. Every paper is about global warming and how high CO2 levels are melting the world. If you come across any other papers on carbon deficiency or depletion I'd love to read them.

Also, I bathed my pH probe in 1:10 bleach for about 25 minutes. It got some of the crud off the pH probe but not everything. During the dip the meter registered 9.4. Then I mixed 5% white vinegar and 91% isopropyl alcohol in roughly 50-50 ratio. It seems to have taken off a little more of the brown staining on the glass. The pH meter read 6.4 during this treatment so it is definitely registering a change which means it isn't broken. Perhaps if I can finish cleaning off all the brown staining on the glass I can finally get it working and calibrate it.

I might try some drain cleaner on it next HCl and see if that will pull off any of the deposits.

It shouldn't hurt the probe since the probe is meant to measure acids and bases anyway.

Any other ideas on what chemicals to use to remove the stubborn deposits would be appreciated!

**edit* 
*

Good news everyone! I used 15 mL of pure H2SO4 (sulfuric acid drain cleaner) on the probe and it completely removed the build up instantly and digested away all the brown staining all the way up the plastic probe. The thing looks brand new now. The glass is good as new. Visually anyway. The pH meter read the pH of the sulfuric acid as 1.9. So I think the probe is functional and now just needs to be calibrated. I'll see what happens when I calibrate it.


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## Zapins (Jul 28, 2004)

Well bad news for the probe. I attempted to calibrate it according to the instructions for the SMS122 but the calibration hole won't let me set the pH to the correct value.

http://www.milwaukeetesters.com/pdf/SMS110-SMS120-SMS122.pdf

I put the pH probe in 7.000 calibration fluid and then twisted the OFFSET calibration trimmer in the hole on the front, the lowest value it would let me do is 7.3. I even tried the rear SLOPE calibration trimmer on the back (which is supposed to be for calibrating to 4.000) and that wouldn't let me bring the pH to 7.0. I tried all the solutions, the 4 the 7 and the 10, and only the 10 value could be set. All the other calibration values wouldn't appear on the controller screen for some reason.

I don't know if this means the probe itself is damaged from years of sitting around in a tank, or if it means the controller itself is damaged.

Either way I won't be testing the pH of anything anytime soon with this setup.

I'll have to see if I can find a cheap digital pH meter.


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## rjordan393 (Nov 23, 2012)

I would expect a probe that old not to function properly. But I based that on information from "American Marine" the distributor of the Pinpoint pH Meters and probes. But what you can try is to let the probe sit in #4 solution for a few days and then see if it calibrates.


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## Tugg (Jul 28, 2013)

You could possibly try this:
http://www.ph-meter.info/pH-electrode-rejuvenating


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## Zapins (Jul 28, 2004)

I'll give it a try with H2SO4 instead since that is the only acid I have on hand. I do have HCl at home but that is several hours drive from my apartment. Though rjordan393 might be right, this pH probe is old as old can be. I don't think I ever actually replaced it and I bought the pH controller maybe 10 years ago?

I don't think I can refill the pH probe I have, there doesn't seem to be any hole to fill it up with fluid like the high quality probes have.


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## Charlie 1 (Aug 24, 2007)

Why not pick up a new probe from flea bay @ 9.00. I have used them before & they work well.


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## Zapins (Jul 28, 2004)

The probes for my controller cost 40 bucks on ebay from what I saw do you have a link to what you found?


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## Charlie 1 (Aug 24, 2007)

Zapins said:


> The probes for my controller cost 40 bucks on ebay from what I saw do you have a link to what you found?


Any probe with a BNC connection will work,
http://www.ebay.com/itm/PH-Electrod...800?pt=LH_DefaultDomain_0&hash=item20d2aae9c8

http://www.ebay.com/itm/VERNIER-pH-...050?pt=LH_DefaultDomain_0&hash=item1c41277092

http://www.ebay.com/itm/Aquarium-Ph...436?pt=LH_DefaultDomain_0&hash=item27c1a5976c


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## Zapins (Jul 28, 2004)

Nice find! I didn't know that the connector's name was BNC.

It is too bad that all the sub-$25 probes are from china (1-2 month shipping time) especially since I only need the probe for one experiment.


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## Charlie 1 (Aug 24, 2007)

Zapins said:


> Nice find! I didn't know that the connector's name was BNC.
> 
> It is too bad that all the sub-$25 probes are from china (1-2 month shipping time) especially since I only need the probe for one experiment.


This one is not & you can make an offer
http://www.ebay.com/itm/Aquarium-Ph...436?pt=LH_DefaultDomain_0&hash=item27c1a5976c


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## Charlie 1 (Aug 24, 2007)

Support your neighbours 
http://www.ebay.com/itm/Replacement...265?pt=LH_DefaultDomain_2&hash=item2a23071d61


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