PH Probe trouble shooting - The Planted Tank Forum
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post #1 of 16 (permalink) Old 04-20-2018, 11:59 AM Thread Starter
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PH Probe trouble shooting

Trying to figure out if my PH Probe is bad or the controller itself-

What I've done-

Put probe into PH7.0 test solution and adjusted controller

Put Probe into PH4.0 Test solution for extended time and adjusted controller

Cleaned probe tip and wiped dry before putting into test solution

Inserted probe back into tank- get PH reading of 5.8 (also low PH reading when just exposed to air)

Confirmed PH of tank at 7.5 via PH test pen and two liquid PH testers.

Other notes-PH Controller seems "flaky" while I was moving it to read it, the PH jumps around on it-not sure if this is normal or not. The Ph Pen is about 6-8 months old and has been underwater the whole time.
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post #2 of 16 (permalink) Old 04-20-2018, 01:39 PM
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Which system do you have? If it is more scientific-grade, then:

When you adjust are you using two different adjustment knobs (one for 7, one for 4)? If not, then adjusting for 4 after adjusting for 7 doesn't seem right.

Can you see either the mV readings instead of pH or the "slope" of the calibration? Both of these help diagnose but often aren't available on "hobby" grade equipment. The mV reading should change greatly between 4 and 7 while the slope should be near a value 60mV/pH unit. A proxy for all of this might just be telling us how far off the 4 value is before you adjust. If it still says something near 7 then the probe is probably bad.

To the "flaky" issue - if the probe is not in a buffer or test solution then the reading isn't relevant - the thin film of water on the probe can change rapidly and the connection to the circuit might be broken during that time as well.

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72g bowfront planted, CO2, 4x - T5HO, Eheim 2213 and 2217, 2 angels, pristella tetras, blue tetras, betta, albino bristlenose pleco, albino cories. Sword, vals, hygros, ludwigias, java moss and fern, anubias

2g Mac-quarium. Clown gravel, fluorescent plastic plants, and 2 guppies.
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post #3 of 16 (permalink) Old 04-20-2018, 02:01 PM
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Trust is needed! When you calibrate the controller by doing first one setting and then calibrate with the other setting using the second adjustment the reading of the tank water will be close enough for our use and the other test methods are not as likely to be correct as the controller as there is no way to calibrate them.
Calibrated versus non-calibrated? Take the calibrated!
But there are ways to mess it up. Make sure to test in different spots of the tank as it can vary. Always store the probe wetas the glass at the tip is not just simple glass and once dried it will have to be replaced to get the correct reading. This is not the current problem as you can calibrate it. Don't let the probe tip get dirty or lay against the tank side, etc. as that will skew the reading.
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post #4 of 16 (permalink) Old 04-20-2018, 03:25 PM
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Maybe try to clean the probe with white vinegar, then rinse and calibrate as usual. Worth a shot.
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post #5 of 16 (permalink) Old 04-20-2018, 04:18 PM Thread Starter
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When I was calibrating it, the probe wasn't off at 7PH and slightly off at 4PH, was reading 3.9 or 4.1 if I remember correctly.

The tip hasn't dried out-still has fluid in it and has been in the aquarium the whole time outside of being clean or tested.

Its mounted to the glass via a clip, not touching anything.

The flakyness happens while it's in the aquarium
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post #6 of 16 (permalink) Old 04-20-2018, 05:02 PM
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Quote:
Originally Posted by Sherminator View Post
When I was calibrating it, the probe wasn't off at 7PH and slightly off at 4PH, was reading 3.9 or 4.1 if I remember correctly.

The tip hasn't dried out-still has fluid in it and has been in the aquarium the whole time outside of being clean or tested.

Its mounted to the glass via a clip, not touching anything.

The flakyness happens while it's in the aquarium
Try turning off the aquarium lights (and maybe everything else electrical). I had an issue of flaky-ness with a probe years ago and I found the lights were causing interference.
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72g bowfront planted, CO2, 4x - T5HO, Eheim 2213 and 2217, 2 angels, pristella tetras, blue tetras, betta, albino bristlenose pleco, albino cories. Sword, vals, hygros, ludwigias, java moss and fern, anubias

2g Mac-quarium. Clown gravel, fluorescent plastic plants, and 2 guppies.
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post #7 of 16 (permalink) Old 04-24-2018, 02:04 AM
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Anyone using one of the DoWhat? Controllers? I had some problems with electrical noise causing erroneous readings on other PH meters in the past - their units have double junction probes and the sensors are electrically isolated - PH readings are spot on with no calibration required. http://dowhatbox.com/product/aquatic-envirobox-sensor-and-power-control-system-with-ph/
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post #8 of 16 (permalink) Old 04-24-2018, 07:09 PM Thread Starter
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I did some more testing-I even put the probe into my smaller tank next to it and it still was reading really low PH-it eventually settled down to 1-2PH, when the tank is around 6.5!

I shut off all electrical connections and it made no difference. I have another probe coming today-see if that fixes the issue.
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post #9 of 16 (permalink) Old 04-24-2018, 07:15 PM
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Quote:
Originally Posted by Sherminator View Post
I did some more testing-I even put the probe into my smaller tank next to it and it still was reading really low PH-it eventually settled down to 1-2PH, when the tank is around 6.5!

I shut off all electrical connections and it made no difference. I have another probe coming today-see if that fixes the issue.
What a bummer. Most of them are rated for at least 6 months but I've found that to be extremely conservative. Seems you did everything you could to troubleshoot. Sometimes you just get a dud. Hopefully the replacement will last you much longer.
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post #10 of 16 (permalink) Old 04-25-2018, 03:51 PM Thread Starter
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I got a new American Marine PINPOINT pH Probe in yesterday-set it up and it read the PH correctly within 30 seconds of being in the water. I haven't had much time to mess with it (i.e. move the controller to see if the readings fluctuate-had an old friend over last night), but its keeping the PH at 6.7 as of this AM when I left for work with the CO2 setup I have.
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post #11 of 16 (permalink) Old 04-25-2018, 09:54 PM
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Something missing here if we are able to read the two calibrated fluids correctly but not the tank water. Not using the same pot to set the meter for the 4.0 as the 7.0 as there is a second pot on the back? The idea of calibrating is to make certain the meter and probe can work at levels between 4 and 7, so something is missing on the idea.

Last edited by PlantedRich; 04-26-2018 at 01:11 AM. Reason: correcting PC weirdness?
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post #12 of 16 (permalink) Old 04-25-2018, 10:24 PM Thread Starter
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Quote:
Originally Posted by PlantedRich View Post
Something missing here if we are able to read the two calibrated fluids correctly but not the tank water. Not using the same pot to set the meter for the 4.0 as the 7.0 as there is a second pot on the back? The idea of calibrating is to make certain the meter and probe can work at levels between 4 and 7, so something is missing on the idea.
There are two pots on the Milwaukee unit, but adjusted to proper PH with old probe

Put old probe into two different tanks and the PH readings would drop under well 4PH

Install new Probe-PH reading of tank (PH 7.5) registers on Milwaukee meter within 60 seconds.

I'm thinking that there is a crack in the old probe or something that only affects it when its almost completely under water.
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post #13 of 16 (permalink) Old 04-26-2018, 01:09 AM
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Okay, new idea!
There are times when things are out to get us and this may be one of those. I propose the idea that there is a tiny crack in the glass on the probe. This crack doesn't open and affect the reading when it is in shallow water like in a test solution but does open a bit more when put into deeper water!
In the olden days of wired telephones, we had something like this called a "high open". The wire was open circuit enough to not allow conversation but would still pass enough higher current to ring the phone! Phones could ring but you couldn't talk.
Maybe try testing the idea before junking the old probe? If it can read near the surface but fails as it is deeper, you verify that you have not lost your mind.
Just been dealing with GREMLINS!
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post #14 of 16 (permalink) Old 04-26-2018, 11:25 AM
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pH probes need to stay wet in order to work correctly, don't dry them off or let them dry out. See this article on probe maintenance (offsite) - "Maintaining and Calibrating pH Electrodes and pH Probes"

pH probes are usually good for about 18 to 24 months. If you can easily calibrate them you can use them beyond that. However, they are something you just need to replace from time to time.
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post #15 of 16 (permalink) Old 04-27-2018, 03:02 PM
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Quote:
Originally Posted by DaveK View Post
pH probes need to stay wet in order to work correctly, don't dry them off or let them dry out. See this article on probe maintenance (offsite) - "Maintaining and Calibrating pH Electrodes and pH Probes"

pH probes are usually good for about 18 to 24 months. If you can easily calibrate them you can use them beyond that. However, they are something you just need to replace from time to time.
Agree with much of this but the part that has me wondering is that they are able to measure and calibrate using the test solutions for both 4 and 7 but not the tank water. Something strange in that.
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