# Different PH Values in the tank



## zozo (27 Jun 2015)

This week i calibrated my PH meters on permanent meter and 1 pocket meter.. I use them for cross reference, they both are never more then 0.5 point off from each other.

Now my permanent meter is in the back left corner and suddenly i see a PH drop to 5.6 and wondered, calibrated both again and it was OK. Took the pocket meter and did put that in diagonal opposit corner and it did read 6.3.
Now took the permannent probe and did put it in the same corner as the pocket one and both read the same.

If i take the pocket one and put it in the place where the permanent one is it read 5,7 to 5.8 it doesn't go as deep as the other.

In the back left the probe is somewhat shielded from view by the Echinodoris and ectualy i've never noticed it dropping so low before. Now i hang the permanent probe 15 cm more to the front in the mid side it read 6.3 as it should. put it back in the corner and it drops back to 5.6 that was all yesterday..  I left the probe in the mid side during the rest of the day.

Today i did put it back in the corner spot and it stays as is 6.4 now..

I realy wonder what could cause such a sudden PH drop in one specific corner of the tank. It defiances my logic and goes beyond my chemistry understanding. Can a plant do that at certain given time, make it's surounding more acidic? If it would be a co2 isue why isn't it permanent and fluctuating incoherent in that corner. It's just a 43 liter tank with sufficient flow. Almost 1 point off in a 15 cm range in about less than 1/6 of the volume of the tank?

Did/do others experience this too is there a logical explanation for this?


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## alto (27 Jun 2015)

Remove samples of water from each area & test in a "still" container (no flow factor on membrane) - make sure to use a clean glass (use plastic if it's what's on hand) container to remove a cup or so or water from each zone, then rinse your "measuring container" 3 times with each solution before filling & checking pH ...

Check your pH meter manuals for details re how long to immerse probe before taking measurement (ie membrane reaction time), there should also be precision & accuracy data available for the pH probe & for the meter (also "drift")


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## zozo (27 Jun 2015)

I did and currently every corner is stable in reading.. The permanent probe has

Alkali Error : 0.2PH (25℃)
Theoretical Percentage Slope : *≥98.5*%
Internal Resistance : ≤250MΩ (25℃)
Response Time : ≤*2*S (25℃)

The Pocket Pen meter has non of these discription in the manual. Is failry slow compared to the other but read the same values after a fresh calibration this goes i bit off as time goes by but not drasticly it stays in a proper range.

It's not in the devices i guess or else they would be off in the calibration as well and that was spot on correct.

I just wonder what could cause such a drastic sudden drop in one corner of such a small invironment. Could i be a build up of something suddenly leaking out of the soil?
Now i remember putting some small clay balls in there 4 months ago under the Echi.. It's my first high tech setup and the tank is still young about 3 to 4 months now and spot on clean. But in a way i don't see the possibility of a Co2 accumulation in one specific corner doing that. I even saw fish hanging in that corner with that reading and not behaiving differntly. It was rather strange experience.


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## X3NiTH (27 Jun 2015)

I've seen similar skewed readings (not as large as the difference you are seeing mind) with two pH controllers in the same tank, figured it to be Stray Voltage after testing the water with a multimeter and got a voltage indication, after isolating things connected to the mains around the tank found it was the pump skewing my readings, the probes themselves added a little stray voltage (about 0.25v) the magnetic fields generated by the pump impellor were adding extra stray voltage which fluctuated slightly depending on how clean the filter was. Another problem with the probe readings were that they were exacerbated by the water having a near zero KH which makes an accurate reading difficult due to the low conductance of the water, this conductance would also change slightly when the EI salts were added every day. I never moved the probes around, I left them situated next to each other just before the filter outlet (shortest route through the water to the pump which is why even with low conductance of the water I was getting stray voltage readings from the pump).

I eventually managed to get the probes to both give me the exact same reading in synchronicity on rise and drop give or take 0.01/2 pH points, I managed this by adding and keeping some KH in the tank which made the readings less fuzzy on the far end of the pH drop (before adding KH the probes would record the pH drop in synchronicity until near the bottom end of the drop when one probe would then go 0.1pH beyond the other and tell me something very different to what the drop checker was saying). I also angled one probe slightly away from the other in its mount and let it lean against the stainless mesh guard on the filter outlet, this also appeared to help mitigate the probes interaction with each other and the stray voltage (two different make probes, not sure if either are sufficiently grounded). 

Another thing I did was to calibrate both probes with their own and each other's reference fluids, one controller has two point calibration at pH4 and pH7 and the other only for pH7, the one that only does pH7 still read the pH4 reference solution of the other controller with an accuracy of 0.01/2pH points, telling me both controllers were giving me functional readings. The first probe went in the tank correctly calibrated and gave me a reading, the fun began when the second calibrated probe went in and gave a different reading, this probe in the tank is the one that appeared to skew the most away from what the other controller and drop checker was telling me so I took the bold step to re-calibrate this probe to read the same as the first probe (the one with two point calibration point pots) whilst in the tank (just turned the pot until it read the same as the other controller), to my surprise it all fell together and I got about 6-8 weeks of synchronicity out the two controllers with an accuracy of 0.01/2pH points from each other before the readings skewed slightly from each other and the whole lot had to be re calibrated again to the reference solutions and then again in tank with one controller, got a good degree of accuracy again the second time around but not as closely synchronised as the first time.

That's my journey trying to work out why two correctly calibrated measuring devices were contradicting each other.


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## zozo (27 Jun 2015)

Thanks for your time to elaborate on your experience..  It explains things. It could indeed be something like electrical interferance.. Some time back i noticed a 0.2 difference on the permanent controler whit using an other so called 12 volt powersupply. I measured the powersupply output and it gave 12.20 volts and the original on gives 11.40 volts.
It could have been a mains fluctuations, power surge or something..

Now a deviation of 0.2 is acceptable and nothing to worry about, but the full point sudden drop was rather mysterious and luckely a drop then the Co2 stops anyway. Rather that than a Ph going up like that out of range would be deadly when not at home.  Ill keep an eye on all electrical equipmentt.. I just baffled me about the measurent went correct again with repositioning the probe with only 15 cm.


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## alto (27 Jun 2015)

zozo said:


> It could indeed be something like electrical interferance..


Yup - that's why I suggested you remove samples from the tank to measure in a "remote location"


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## zozo (28 Jun 2015)

That's what i regularly do with the pocket probe, because it's slow reacting, so i can dip it and wait. I guess i'll have to wait till the next time i see it happen it is'nt constant. And still it wonders me, if it was an electrical interferance from outside why only that particular area in such a small tank is affected.

That's why i asked the question, maybe some people noticed something like that too and maybe have an biochemical explanation.. Like maybe it's another compount in the water where a PH meter could react with. Comming from a plant or the soil I don't know of (yet). Lately i saw a stream of realy tiny bubbles coming up like a tiny string of pearls rising to the surface wittnessed it for minutes and i thought it was oxygen from a plant. I do not know i couldn't find the originating spot in the dense growth if it was the Enchi or the Lilaepsis or the soil. Actualy saw it happen 2 times in the same corner but that was weeks ago..

Maybe i witnessed a little rare wonder of nature there. Or just something realy simply explainable.. Who knows?


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## dw1305 (28 Jun 2015)

Hi all,





zozo said:


> It could indeed be something like electrical interferance.


 Electrical interference does effect pH reading. From <http://www.asi-sensors.com/ASI/learning/pH_FAQ.pdf>





> The high resistance and low current signal of a pH electrode is extremely susceptible to electrical interference. Inductive and triboelectric noise are the two main types of interference. Inductive noise is generated by moving electrical fields near the cable, an electric motor varying in speed or a person walking by wearing clothing with a high static charge can influence the electrode reading. Triboelectric noise is a static discharge in the cable caused by moving the cable.





zozo said:


> Lately i saw a stream of realy tiny bubbles coming up like a tiny string of pearls rising to the surface


 Oxygen is a base, so high levels of dissolved oxygen will cause the pH to rise, in the same way that high levels of CO2 will make pH fall.

cheers Darrel


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## zozo (28 Jun 2015)

Thanks Darrel,

That's what i'm trying to figure out now. 

I guess logicaly it must be something electrical, whit such a small thank everything is very close togheter try to find me another more nutral position for the PH controler. But the probe stilll will be near the lights as possible interfaring power source. You would expect something constant or more freqeunt if it was something like that. Or maybe it was me having BBQ with a wrong batch of charcoal and buzzing everything of the scale. That was a strange spike of strange readings..

The relations of oxygen, co2 and KH levels don't make sense to me in this case, because that sudden drop would mean a very hihg co2 accumulation or KH drop in just that corner at that time.

I'm just not sure enough of myself to state certain things are impossible..  I'll keep an eye on it..


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## pepedopolous (29 Jun 2015)

Hi guys,

I've noticed that my pH meter gives and unstable reading when too close to the flow pump: -




If I put the meter in the opposite corner, I get a stable reading.



Cheers,

P


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