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Reefocd
04/26/2013, 12:56 PM
Simple question,

New probe, new fluids. Is the idea if settles close to but no cigar to say, 6.98 and 10.08 and we are to true up the numbers to 7.0 and 10.0.? Have to trust the probe or fluids, right, else why have ability to tweak numbers on controller...

Do I have the concept right?

Thanks!

kurt_n
04/26/2013, 03:02 PM
Correct. The number you see on the controller isn't supposed to be an indication of the pH of what its in when you are calibrating. It should be close, but as long as it has settled you're OK.

Reefocd
04/26/2013, 03:26 PM
Not sure I understand? Why wouldn't the number settle to the fluid it's in? My question, if I follow the fluid parms to the tee and it should be 7.0 at x degrees and x salinity, but the controller reads 7.09, should I manually sync value to 7.0? Which means I am choosing fluid to be gospel so to speak. Can't have it both ways, can we? Either we trust the probe at 7.09 or it's wrong and we trust the fluid....

Thoughts?

Daimyo68
04/26/2013, 05:35 PM
Perform the calibration as stated in the manual. Don't worry about the numbers you see on the screen, yet. Let the numbers settle and then finish the process.

---Now go back to the home screen, put your probe in the 7.00 fluid, the pH on the Apex should read 7.0
---Rinse the probe off in RO/DI
---Now put the probe in the 10.00 fluid, the pH on the Apex should read 10.00

I calibrate using 7.01 and 10.01 fluids and after calibration, it's always dead on. There can be temp variations, but the packaging usually states what it should read at xx temp

Daimyo68
04/26/2013, 05:37 PM
Perform the calibration as stated in the manual. Don't worry about the numbers you see on the screen, yet. Let the numbers settle and then finish the process.

---Now go back to the home screen, put your probe in the 7.00 fluid, the pH on the Apex should read 7.0
---Rinse the probe off in RO/DI
---Now put the probe in the 10.00 fluid, the pH on the Apex should read 10.00

I calibrate using 7.01 and 10.01 fluids and after calibration, it's always either within .02 or dead on. There can be temp variations, but the packaging usually states what it should read at xx temp

kurt_n
04/26/2013, 10:47 PM
...Which means I am choosing fluid to be gospel so to speak...

Yes. You are. That's the definition of "calibration fluid" - fluid that is known (assumed) to be at an exact value.

The number you are seeing is just the internal voltage value that the probe is reading. It could just as well read 125678 when its in the 7.0 fluid - it means the same. The process is that the controller takes the voltage the probe is reading when it's in the 7.0 fluid and assigns that value a pH of 7.0. Then when you stick it in the 10.0 fluid it assigns that voltage a pH of 10.0. The controller then calculates the slope of the line between those two points so that it can give you an exact value for any voltage reading that lies between the 7.0 and 10.0 solution. The calibration fluid IS Gospel... that's its purpose. The probe and controller are dumb - it needs the calibration fluid to tell it what is what.

The only reason the Apex gives you number in the display when you're calibrating is to make sure it has leveled off (settled) before moving on to the next step. It really means nothing.

And yeah... do what Daimyo68 said, and you'll be spot on! It's important to rinse the probe in RO/DI (and shake the excess off) when going between different calibration fluids because you don't want any excess 7.0 fluid getting into the 10.0 fluid and changing the value of the pH in that packet.

Reefocd
04/27/2013, 01:20 AM
Now I get it.Thanks guys for the great description of the calibration process.

Reefocd
04/29/2013, 12:22 PM
Update:

New calibration fluids did the trick. Had to go through process twice. 10.01 fluid works perfect each time, however, 7.01 fluid settled at 7.70 first time and 7.6x second time. When put back in 7.01 fluid, eventually measured 6.99, close enough. Ph is 8.4x ish in day and 8.27ish at night . Gonna play with kalk reactor / top off at night to reduce that swing .....

Thanks all!

AZRippster
05/01/2013, 01:35 PM
Here is a weird thing I have noticed.

I have 2 pH probes. One is used in the sump for the tank's pH and another in my calcium reactor to control the CO2 valve. The other day while doing maintenance, I decided to clean and recalibrate both probes as it had been awhile. I calibrated both but found that afterword, while both were in the sump (not the CO2 reactor), their readings were different by .12. One of the probes is the Neptune Lab Grade and the other is a Milwaukee Instruments. I thought this was odd, so I placed each one in the 7 and then 10 pH calibration solutions to see what they read. Both read spot on! After rinsing and returning to the sump, they returned to a variance of .12. I repeated the calibration process on both probes and returned to the sump to find once again they were .12 different. BTW, the Milwaukee was the one reading .12 lower than the Neptune. As a side note, they were in the sump reading the same water but about 10" apart so I don't believe there was any interference causing the variance.