Ph probe calibration

ReefKeeperElite · Oct 11, 2017

Hi all.

Just doing my quarterly calibration. It's always taken around 3 hours for the 7.0 calibration raw data to stabilize. Same today, but never really asked around before.

Is the the case for others? The 10.0 stabilizes much faster, around 20 minutes.

Setup:

Brand new lab grade BRS probes.
DA Reefkeeper Elite controller.
BRS Ph probes on both DA SL1 and SL2 modules.
Brand new Milwaukee 7.01 and 10.01 calibration fluids.
Probes are tightly sealed in calibration satchels to mitigate atmospheric changes.

TIA

AdamNC · Oct 11, 2017

I run the Apex and it stabilizes in about 5 mins. using the Milwaukee fluid also.

Randy Holmes-Farley · Oct 11, 2017

What level of drift are you trying to avoid by waiting that long? 0.01? 0.001 per min? It should not take that long.

Are you near any electrical interference?

dealseer · Oct 11, 2017

Mine takes 15-20 minutes

Randy Holmes-Farley · Oct 11, 2017

Is the ongoing drift always in the same direction? Which direction?

If the probes were not brand new, I'd say clean them by soaking in acid, and that might help anyway.

ReefKeeperElite · Oct 11, 2017

The SL1 starts out at a raw data reading of 430, then slowly drifts down (just one direction) to 275/285 over the next 3 hours. The probes are brand new, as is the fluid.

Randy Holmes-Farley · Oct 11, 2017

ReefKeeperElite said:
The SL1 starts out at a raw data reading of 430, then slowly drifts down (just one direction) to 275/285 over the next 3 hours. The probes are brand new, as is the fluid.

What does that translate to in pH? Do you not see pH readings in real time during calibration?

ReefKeeperElite · Oct 11, 2017

I can see the ph on the DA NET webserver at the same time, which is presumably based on my previous calibration 3 months ago. The raw data above translates to a ph of 7.15 (raw = 430) to a ph of 7.03. (raw = 280).

Randy Holmes-Farley · Oct 11, 2017

ReefKeeperElite said:
I can see the ph on the DA NET webserver at the same time, which is presumably based on my previous calibration 3 months ago. The raw data above translates to a ph of 7.15 (raw = 430) to a ph of 7.03. (raw = 280).

OK, so the question, how far along that path is it after, say 30 minutes.

ReefKeeperElite · Oct 11, 2017

After 30 minutes the raw data will be in the lower 300's, maybe 310-315. Then will slowly keep going until 275/285. I come back every 10 minutes to see if the raw data changed since my previous check. If it does, I make note of the new range of readings (hi/lo), walk away for another 10, and so forth, until the hi/lo are in the same range. I don't want to save until the final two ranges are the same.

Randy Holmes-Farley · Oct 11, 2017

ReefKeeperElite said:
After 30 minutes the raw data will be in the lower 300's, maybe 310-315. Then will slowly keep going until 275/285. I come back every 10 minutes to see if the raw data changed since my previous check. If it does, I make note of the new range of readings (hi/lo), walk away for another 10, and so forth, until the hi/lo are in the same range. I don't want to save until the final two ranges are the same.

Is the temperature changing? That alters the reading.

I'd try soaking the probe overnight in vinegar. Maybe it dried out at some point (which ruins them).

here's my section on calibration:

http://www.advancedaquarist.com/issues/feb2004/chem.htm

4) It takes some time for a pH meter to get a correct reading. So let the meter equilibrate to each standard long enough that the value stabilizes (say, within +/- 0.01 pH unit for 30 seconds or longer). Some meters beep or otherwise tell you when you are suitably equilibrated.

5) Stirring the solution can help the pH probe equilibrate to the solution, but it also encourages CO2 to enter the fluid. This CO2 can lower the pH of high pH standards, such as pH 8 and greater. I stir mine for about 30 seconds (often with the pH probe itself, though I've also broken them this way) and then let it sit to get a reading.

ReefKeeperElite · Oct 11, 2017

Wow that's an awesome article Randy, thanks for sharing!

My temp stays consistent during testing, but I had been swooshing around the solution between readings. Don't know why exactly, but your explanation of inviting CO2 will make me stop doing that. Actually will try again tomorrow without swooshing.

Will keep in touch on that and anything else which may help solve this issue. At any rate, thank you so much for taking the time to help me out!

Randy Holmes-Farley · Oct 12, 2017

You're welcome.

Good luck!

ReefKeeperElite · Oct 12, 2017

Quick update.

Turns out that not touching the fluids once the calibration period started had a big affect. It took 30 minutes per probe. They are now both in lock step with each other too, currently at 8.04

Now I have to work on getting the ph within 8.1 - 8.3. The 8.04 showing here is too low. It’s midday here, and would think it should be around 8.2.