pH Calibration Procedure

[NeonRabbit221B]

Can anyone share their calibration procedure for pH? I feel like every other calibration makes the sensor go crazy. I typically use the bottled solutions and pour about 80 ml into. a specimen cup and wait 1 minute and give it a swirl or two during the 1 minute wait. Just not sure I trust that my tank is suddenly 7.65

 

[MnFish1]

Which test are you using - what are you trying to calibrate?

 

[NeonRabbit221B]

Reef-pi ph probe with ML pH board and Milwaukee probe.

 

[MnFish1]

Can anyone share their calibration procedure for pH? I feel like every other calibration makes the sensor go crazy. I typically use the bottled solutions and pour about 80 ml into. a specimen cup and wait 1 minute and give it a swirl or two during the 1 minute wait. Just not sure I trust that my tank is suddenly 7.65

Thanks - does the meter read correctly when you calibrate (i.e. using the solutions). The solutions I use are in a single use envelope - which means that there is no chance for contamination.

Also - the best way to figure out whether its probe problem or something else is to just use a different method to compare pH.

It remains unclear (to me) - what your second sentence means 'every other calibration makes the sensor go crazy'.

 

[MnFish1]

PS here is a similar thread discussing your problem:

Help with Calibrating PH Probe

No problem, I feel bad about it all. I have to disagree with not having to replace it, you've done nothing wrong. Yeah I was referring to dropping in the whole board, there's 7 screws holding it in place, remove them and it'll lift out. Thankfully the cost isn't too bad, it's more about the...

www.reef2reef.com

 

[NeonRabbit221B]

I appreciate the link. Essentially I have calibrated this probe with a variety of solutions over the 2 years I have had it. Sometimes results match up with test kits or my pen style but half of the time the value is significantly lower than expected.

What I was looking for was like a detailed process of calibration. Do you heat the solutions to tank temp? Do you clear the electrode before? How long do you let the probe sit in the solution before accepting the value?

 

[minus9]

You need to keep the solution in the tank to maintain temp during the calibration process, then proceed with calibration. I think you can just check/verify that the pH probe is correct by just testing it in a known solution and calibrate if it's off. No need to calibrate if it's measuring correctly.

 

[NeonRabbit221B]

So I tried it twice maintaining temp and my milwakee was still reading as low at 7.6 today. I swapped the probes and retried it and now its reading 8.6... Any recommendations for known solutions that are not the 7.0 and 10.0 solution?

 

[robsworld78]

Not sure why you are experiencing this but for calibration 7.0 should always be used for the 1st point and if you do dual point calibration the 2nd should be 10.0 or there about. 4.0 is ok as well but the results are better if the buffers are within the range expected.

Things you like know but be sure to leave the probe in the solution until the reading becomes stable, depending on probe it can take 3-10 minutes, don't rush this. When you take the probe out of the buffer solution dip it in some clean water and flick off the excess water so it doesn't contaminate the next buffer. Here's a link with some times on cleaning a probe, maybe it needs that.

How to Store, Clean, and Recondition pH Electrodes from Cole-Parmer

Taking care of your pH electrodes will ensure proper functioning, as well as enhance their longevity. Read more in this informative article from Cole-Parmer.

www.coleparmer.com

 

[NeonRabbit221B]

Not sure why you are experiencing this but for calibration 7.0 should always be used for the 1st point and if you do dual point calibration the 2nd should be 10.0 or there about. 4.0 is ok as well but the results are better if the buffers are within the range expected.

Things you like know but be sure to leave the probe in the solution until the reading becomes stable, depending on probe it can take 3-10 minutes, don't rush this. When you take the probe out of the buffer solution dip it in some clean water and flick off the excess water so it doesn't contaminate the next buffer. Here's a link with some times on cleaning a probe, maybe it needs that.

How to Store, Clean, and Recondition pH Electrodes from Cole-Parmer

Taking care of your pH electrodes will ensure proper functioning, as well as enhance their longevity. Read more in this informative article from Cole-Parmer.

www.coleparmer.com

Thanks for the link Rob! Fourth attempt seemed to get me something within reason switching back to Milwaukee probe. Cleaned with bleach, light brushing, muratic acid and swung it around. I let the probe sit for a full 10 minutes and stirred it every 3-4 minutes until it finally stabilized. I will check back in 24 hours and do some crappy API tests as a sanity check.

One question, any low risk way of matching tank temp to the solution? Felt nervous clamping a cup inside my sump. If it spills.. large water change? I think its phosphate based solutions.

Appreciate the help!

 

[robsworld78]

Thanks for the link Rob! Fourth attempt seemed to get me something within reason switching back to Milwaukee probe. Cleaned with bleach, light brushing, muratic acid and swung it around. I let the probe sit for a full 10 minutes and stirred it every 3-4 minutes until it finally stabilized. I will check back in 24 hours and do some crappy API tests as a sanity check.

One question, any low risk way of matching tank temp to the solution? Felt nervous clamping a cup inside my sump. If it spills.. large water change? I think its phosphate based solutions.

Appreciate the help!

No problem, glad it was helpful. If you're just swapping probes and the reading is ok something must be up with that probe. Also note the calibrate is tuned to the probe, if you change probes you have to recalibrate.

Yeah probably need to be careful not getting any of that buffer in the tank, don't worry about the temperature, although it affects things if the temp is between 20 - 30 Celsius it has little effect. The formula to calculate pH uses 25c unless otherwise stated that's why the buffers say 7.0 @ 25c. So instead of trying to match buffer to tank ideally you want it at 25c.

The other day I actually typed out an example of how temperature effects pH, I'll paste it here.

pH is voltage based and measured in millivolts. The circuit reads 0mV at 7.0 pH and +/- 1.0 pH = 59.16mV @ 25 Celsius. If temperature compensation isn't used the 59.16mV is what's used to calculate the value. For example lets assume the circuit was reading -89.92mV from the probe, that needs to be converted to pH. If you don't use temperature compensation we get "7.0 - (-89.92mV / 59.16mV)" = 8.519 pH. But what is the pH if the water was actually 30 Celsius not the assumed 25c.

First we offset the 59.16mV doing this "59.16mV * (30c + 273.15) / 298.15" = 60.15mV. Now we run the math to get the pH. "7.0 - (-89.92mV / 60.15mV)" = 8.494 pH instead of 8.519.

 

[Ranjib]

I used to use 7, 10 and 4 ph solution based on what setup I'm using. For reefing use case, 7 and 10 is sufficient. reef-pi+ opensource ph board can only support one or two point calibration. Temperature compensation is also not supported by the core reef-pi library but that too has limited implication (assuming your ambient temperature is not significantly different (>10F). You can do both of those with ezo circuit, out of band.

In recent times i exclusively use hannah hand held checker, and calibrate the sensor straight in my tank. I run the uncalibrated probes in the tank for a full day to uncover the peak/low times and then just use hanna hand held checker to take reading during those times and then later use it for calibration in one go.

 

[dmsc2fs]

In recent times i exclusively use hannah hand held checker, and calibrate the sensor straight in my tank. I run the uncalibrated probes in the tank for a full day to uncover the peak/low times and then just use hanna hand held checker to take reading during those times and then later use it for calibration in one go.

How are you using the hand held checker to calibrate? Are you manipulating a file on the pi or are you adjusting the values in the input field?

Secondary to that, if the prope is in a known solution and you can just use the "run" button to calibrate, what is the reason for the up and down options on the input? Would that be to change the value of the reference? In case you are not using 7.0 and 10.0 reference solution?

 

[gbroadbridge]

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