pH Calibration -- manual adjustments?

tgreene

tgreene

Reefer
Both of my pH Probes are consistently reading -0.05 of the actual pH, so I need to know how to do a manual overide adjustment.

No matter how many times I've calibrated them, they continue to hold the same values lower values. Both probes are however providing nearly the same readings which is good.

So, how do I do a manual pH calibration override..?

-Tim
 
Hi

Hope you dont mind me asking why do you think they are reading low?, both probes are reading the same therefore on law of averages the reading you are getting is spot on. Therefore your "actual" pH is what they are reading.

A pH probe has a tolerance of +/- .01
 
They are consistently -0.05 low when immersed in pH buffer solution... It doesn't seem to matter what solution strength (4,7,9,10), they are low.

I've also tested against other pH measurement devices, and the fact that both probes read within +/- 0.02 of each leads me to believe that the probes are spot on but the ProfiLux display is errant to the low side.

So, how can this be manually adjusted..?

-Tim
 
Hi

The GHL is 100% accurate in its reading therefore it does not have a requirement for an offset.

If calibrated correctly you can see at the lower points the probe reading slightly away from the lower or high point, this is normal.

Example if a probe is calibrated to 7 and 9 the most accurate point will be 8. If then put in 9 you may see it read slightly low than this.

Furthermore probes are degenerartive, as they get older the tolerenace will increase, this also must be taken into account.

Quality of probe also plays a major factor/reaction time. If using genuine GHL pH probes the tolerence will be far closer than the generic.

You will always see and never be able to match devices, each device will read the probe value slightly differently also.

we are talking about 0.03 of a difference based on the .02 tolerence quoted, at lower point where your tank water should never be at.
 
In the following buffering solutions, these are my current readings:

4.01 -- 3.86pH
7.00 -- 6.87 (GHL Buffer solution)
7.01 -- 6.84pH
9.00 -- 8.86pH (GHL Buffer solution)
10.01 - 9.95pH

As you'll see from the readings, I was actually incorrect, and that the averages are not -0.05, but rather -0.15

The probes are brand new GHL black probes that just came with my new Profilux 3 this past week.

If the controller is 100% accurate as you say, then the 2 different brands of buffer solutions would both have to be inaccurate, as would the new GHL probes and also the other electronic pH testing devices that I have.

-Tim
 
I floated the 2 containers of GHL solution in the tank for about 30 minutes before calibration... They would have been between 78-79 degrees f.

I have some errends to run and will be out for a good hour or so, so I'll try floating them again while I'm gone to attempt a more proper re-calibration. I'll post those results when I'm done.

-Tim
 
Hi

The controller has auto temperature compensation.

This is all within tolerence and also expected as before explained about low/high range reading on dual calibration.

It also shows the GHL calibration solution brings the probes closer to the low/high range end points.

Please be assured your probe/controller/solution is accurate and we are playing with the utmost fine tolerences here at the upper most ends of the claibration scale where all manner of things can creep in such as contamination of fluid - residue of last calibration solution used still within the membrane of the probe - storage solution still precipitating from the probe - not enough time left for probe to settle.

Hope that reasures :)
 
Last edited:
I guess I'll take your word for it, but please note that I am anything but new at this... I've been using controllers fgor years and when calibrating always float my solutions, rinse the probes in pure RO water and pat dry them between immersing in different solutions, and no matter how you slice it -0.15 averaging is beyond my own personal comfort limit.

I'll go ahead and re-calibrate immediately, then again in another week to see if there is a difference since the probes have had more time to "burn in".

Now to figure out how to do all the other stuff that isn't in the manual or mentioned anywhere due to the new software.....

I DO LOVE THE CAPABILITIES OF THIS SYSTEM AND KNOW THAT IT'S THE FINEST OUT THERE, BUT WAS JUST CONCERNED WITH THE pH READING.

-Tim
 
Errrr, ummm, after re-calibrating with the solution that had been floating for just over an hour, both probes calibrated to within 0.01 of the outer ranges, and both provided identical readings to each other.

I feel like such a dolt!

I'm detecting that you willed good karma down across the border. :)

-Tim
 
Glad to hear it worked out :-) Even though the probes should compensate for temperature it never hurts to calibrate with solutions that are the same as the tank (I've encountered similar behavior on rare occasions if the fuilds were cold).

Hope the good karma keeps flowing your way! ;-)
 
We are only here to serve LOL :)

call me any time on EST from 9am to 5pm email me for number, however at present no tech support is offered over the phone
 
You must log in or register to reply here.

Similar threads

Mr31415
Low alk on new tank
2
Replies
29
Views
1K
Mr31415
Mr31415
Reef Kinetics
Exciting Review by Joey Jones of TheCoralReefTalk: New Batch 6 ReefBot Lab
Replies
0
Views
203
Reef Kinetics
Reef Kinetics
T
Issue with Sump and turnover
Replies
2
Views
427
twiddybr
T
JustinGr
PH Issues
Replies
11
Views
1K
Jposch
J
S
Phosphate flow out of live rock
Replies
0
Views
129
SantaMonica
S
Back
Top