Calcium Reactor PH probe calibration

[VJV]

Hi, I am installing my shinny new Calcium reactor (my first) and just realised I bought the wrong calibration fluids for the PH Probe: 7.00 and 10.00 instead of 4.00 and 7.00. Will the calibration be completely off if I use the 7 & 10 calibration solutions? I intend to set the controller (Profilux4) to maintain a PH inside the reactor at 6,7, +/- 0,3.

Many thanks and kind regards

 

[Diesel]

You will be ok.
Next time you be at the LFS or place a order you can recalibrate it with the 4-7 solution

 

[VJV]

Thanks! It is my first reactor and I have several large SPS colonies so am a bit nervous [emoji51]...

 

[Diesel]

Thanks! It is my first reactor and I have several large SPS colonies so am a bit nervous [emoji51]...

Ouch.
In that case test your big three everyday.
You want to be on top of it.
If the CaRx can’t keep up with it due to dialing in you need to manual dose your two part still.

 

[Lasse]

I will try to explain how it works with calibration of these probes. The probe measure the potential difference between the negative OH ions and the positive H ions (in real life the H3O ion but most off you are used of H ions )
If the potential is 0 mV (as many OH as H3O ions) - pH = 7 Normal electrodes use to hav steps from 56 mV to 59 mV between each pH step and it is a negative curve - it means (if the probe have 56 mV in each step) that minus 56Mv= pH 8, minus 112 mV is pH 9 -> + 56 mV = pH 6, +112 mV = pH 5 and so on. The computer into the pH meter (or the ProfiLux) translate the mV that the probe read to pH. The translation curve is rather linear. All probes are not perfect and they will age with time - therefore you need to learn your computer what to expect of different mV reading. This "learning process" is named Calibration. With the 7 pH solution - you just say to your computer - This is 0 mV - whatever!. Now you have a fixpoint at 0 mV(pH 7. But you do not know the slope of the curve. If you now take pH 9 or 10 solution and say to the computer. This is pH 9 (or 10) - now you have two fixed points and the computer can use the straight line between the two fixed points in order to translate any measured mV into pH. Of cause - if you have the line between 0 mV and the mV for 9 or 10 - it will in the world of your computer keep on being a straight line on the other side of 0 mV too. The only difference is that you will have a little better precision if you calibrate between 7 and 4. But you want to measure around 6.5 and that´s rather close to your fixpoint 7 - it will work.

The GHL/ProfiLux use a little different way of explaining what the probe measure - they do not show it as mV. And they always start the calibration process with the lowest value. If you calibrate between 4 and 7 - the calibration process start with 4 - and if you calibrate between 7 and 9 (10) - the process start with pH 7 standard.

I hope that this can help with the understanding of the processes behind pH measurements with electrodes and that you understand that these cheap pH meters that only use one calibration point is a joke.

Sincerely Lasse

 

[VJV]

I will try to explain how it works with calibration of these probes. The probe measure the potential difference between the negative OH ions and the positive H ions (in real life the H3O ion but most off you are used of H ions )
If the potential is 0 mV (as many OH as H3O ions) - pH = 7 Normal electrodes use to hav steps from 56 mV to 59 mV between each pH step and it is a negative curve - it means (if the probe have 56 mV in each step) that minus 56Mv= pH 8, minus 112 mV is pH 9 -> + 56 mV = pH 6, +112 mV = pH 5 and so on. The computer into the pH meter (or the ProfiLux) translate the mV that the probe read to pH. The translation curve is rather linear. All probes are not perfect and they will age with time - therefore you need to learn your computer what to expect of different mV reading. This "learning process" is named Calibration. With the 7 pH solution - you just say to your computer - This is 0 mV - whatever!. Now you have a fixpoint at 0 mV(pH 7. But you do not know the slope of the curve. If you now take pH 9 or 10 solution and say to the computer. This is pH 9 (or 10) - now you have two fixed points and the computer can use the straight line between the two fixed points in order to translate any measured mV into pH. Of cause - if you have the line between 0 mV and the mV for 9 or 10 - it will in the world of your computer keep on being a straight line on the other side of 0 mV too. The only difference is that you will have a little better precision if you calibrate between 7 and 4. But you want to measure around 6.5 and that´s rather close to your fixpoint 7 - it will work.

The GHL/ProfiLux use a little different way of explaining what the probe measure - they do not show it as mV. And they always start the calibration process with the lowest value. If you calibrate between 4 and 7 - the calibration process start with 4 - and if you calibrate between 7 and 9 (10) - the process start with pH 7 standard.

I hope that this can help with the understanding of the processes behind pH measurements with electrodes and that you understand that these cheap pH meters that only use one calibration point is a joke.

Sincerely Lasse

Thanks Lasse! Incredibly useful. I feel a bit better about using the 7&9 solutions to calibrate. As Diesel said I have also ordered the 4&7 solutions from Hanna to fine tune calibration.