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iwishtofish
12/30/2011, 11:07 AM
I finally got around to calibrating my Pinpoint pH meter. I'm wondering if I did it right.

With the probe dipped in the 7.0 solution, the best I could get it to do was flicker between 6.9 and 7.1 (back and forth, back and forth, and so on...). Same scenario with the 10.0 solution - between 9.9 and 10.1.

I calibrated between the two solutions twice, rinsing the probe in RO/DI water, and shaking it gently.

Just incidentally, the probe in my tank reads 7.94. Was I not precise enough with the calibration? Should I order more solution and try again?

disc1
12/30/2011, 11:54 AM
Flickering by 0.2 pH units in the calibration sounds like an interference issue. Does it still flicker over such a range in the tank?

I would recalibrate it, but I still think you did good enough to say it's somewhere around 7.9.

iwishtofish
12/30/2011, 12:13 PM
Flickering by 0.2 pH units in the calibration sounds like an interference issue. Does it still flicker over such a range in the tank?

I would recalibrate it, but I still think you did good enough to say it's somewhere around 7.9.

It doesn't flicker in the tank, although I just did a small water change, and it flew all over the place whenever I turned a pump on or off, or when the main lights came on. A short while later, though, it is right back to 7.94.

disc1
12/30/2011, 12:26 PM
When you did the calibration, did you have the probe in your hand?

What happens if you take a cup of water out of the tank and measure it the same way you did the calibration?


It sounds like it may be very sensitive to electrical interferences.

iwishtofish
12/30/2011, 12:40 PM
When you did the calibration, did you have the probe in your hand?

What happens if you take a cup of water out of the tank and measure it the same way you did the calibration?


It sounds like it may be very sensitive to electrical interferences.

I did. I'll have to try that. I have the probe right next to a Koralia 4, and when I turn that particular pump off, the meter rapidly drops to around 7.85, but then (with pump still off) gradually climbs back to 7.94.

I think you are right about the electrical interference.

disc1
12/30/2011, 12:43 PM
Which model pinpoint is it?

Does the probe have a BNC connector (http://en.wikipedia.org/wiki/BNC_connector) style?

disc1
12/30/2011, 12:45 PM
Also, try running it on battery power and see if that changes anything.

shaggss
12/30/2011, 12:46 PM
yeah the probe should be as faraway from any electrical devise as possible. I use the PinPoint Cal fluids and peg them to the side of the sump with a corner pointing down and only open a hole big enough to put the probe in.

iwishtofish
12/30/2011, 05:44 PM
Which model pinpoint is it?

Does the probe have a BNC connector (http://en.wikipedia.org/wiki/BNC_connector) style?

Also, try running it on battery power and see if that changes anything.

I'm not sure which model. Just pH. Recent, with BNC connector. It's only been run on battery.

yeah the probe should be as faraway from any electrical devise as possible. I use the PinPoint Cal fluids and peg them to the side of the sump with a corner pointing down and only open a hole big enough to put the probe in.

Hmmm...really not sure where to put it. It seems I have electrical devices everywhere.

I'm going to order more fluid, and try calibration as recommended by you and disc1.

Randy Holmes-Farley
12/31/2011, 06:02 AM
When you say flicker, did the numbers move up and down through intervening values (say, 6.90, 6.92, 6.93, 6.94...), or was it an instantaneous jump from 6.9 to 7.1, say?

iwishtofish
12/31/2011, 07:30 AM
When you say flicker, did the numbers move up and down through intervening values (say, 6.90, 6.92, 6.93, 6.94...), or was it an instantaneous jump from 6.9 to 7.1, say?

It appeared to be instantaneous, with both solutions.

Randy Holmes-Farley
12/31/2011, 11:53 AM
That does sound like some sort of electrical problem.

iwishtofish
01/05/2012, 04:46 PM
Alright, here we go again...

http://i211.photobucket.com/albums/bb113/bjdoyle64/pinpoint2.jpg

I'm wondering if the big party cups I placed these fluid pouches inside were holding a static charge. I'll make sure I'm far from electrical devices, and that I let go of the probe when it is inside each pouch.

Any other precautions?

Randy Holmes-Farley
01/05/2012, 04:50 PM
I usually put the probe right into the pouch.

Rinse well with RO/DI before and after each fluid. :)

disc1
01/05/2012, 04:55 PM
The party cups shouldn't be a problem. I've been using those as cheap disposable beakers for a long time. As long as you are taking them straight off the stack, they are surprisingly clean and for the most part sterile.

iwishtofish
01/05/2012, 05:02 PM
I usually put the probe right into the pouch.

Rinse well with RO/DI before and after each fluid. :)

Randy, is it ok to leave the probe turned on between transfers and rinses? Probably a stupid question...

The party cups shouldn't be a problem. I've been using those as cheap disposable beakers for a long time. As long as you are taking them straight off the stack, they are surprisingly clean and for the most part sterile.

I was just setting the pouches inside the cups to hold them, rather than pouring the fluid into them.

Do you think there's a chance the cups hold a static charge that caused interference, or was it more likely my hand? It's strange - during the calibration the meter would flicker, but never when in the tank.

bertoni
01/05/2012, 07:03 PM
Leaving the probe on is fine.

I wouldn't worry about the flickering during the calibration phase, and I think that leaving the fluids in the pouch is a good idea. I always did that, although I used Oakton products.

iwishtofish
01/05/2012, 08:34 PM
Leaving the probe on is fine.

Ok, thanks.

I wouldn't worry about the flickering during the calibration phase, and I think that leaving the fluids in the pouch is a good idea. I always did that, although I used Oakton products.

Yeah, I just wasn't sure how accurate it could be. When I calibrated with the 7.0 fluid, the meter flicked from 6.9 to 7.1. I could never get it to stop at 7.0. Same deal with the 10.0 fluid.

bertoni
01/05/2012, 11:17 PM
Is that 6.99 to 7.01? How many digits does this meter have?

shaggss
01/06/2012, 01:07 AM
Just use a clothes peg a clip the Cal fluid to the sump. then stick the probe in the fluid. easy!

iwishtofish
01/06/2012, 06:05 AM
Is that 6.99 to 7.01? How many digits does this meter have?

It has three digits, so it must have been...funny (or not) how I can't recall! Maybe, then, that would be ok?

Just use a clothes peg a clip the Cal fluid to the sump. then stick the probe in the fluid. easy!

Good idea!

iwishtofish
01/06/2012, 07:08 PM
Ok, calibrated again today, thinking maybe I didn't have to. I had pretty good luck with the numbers holding steady. I got the impression my meter was off a bit. The tank now reads 7.89, whereas before it ranged between 7.94 and 7.99.

I did notice that the numbers began to skew when I went back and forth between fluids, even though I rinsed well between solutions and gently shook the probe of excess water. I wonder if the true way to go is to have two packs of each solution, not using any one twice, thus avoiding cross contamination.

bertoni
01/06/2012, 08:14 PM
You should be using the fluids only once, and switching between them should be done only once. The fluids lose accuracy on contact with the air.

iwishtofish
01/06/2012, 08:53 PM
You should be using the fluids only once, and switching between them should be done only once. The fluids lose accuracy on contact with the air.

Yes, used new fluids (7.00 and 10.00) just tonight, and then tossed them. The PinPoint instructions say to recalibrate between each fluid as many times as necessary, until adjustments are no longer needed. I'd imagine the more that is done, the less accurate each fluid would become! Sounds self-defeating...

bertoni
01/06/2012, 10:35 PM
Interesting. My pH meter required one dip in each solution. Maybe it might have had more of a computer in it to do the coefficient calculation. I can't think of another reason to do multiple calibrations.

Randy Holmes-Farley
01/07/2012, 05:35 AM
It can take several minutes in each fluid, but once is usually appropriate. Then when done, it is fine to check them in the fluids again. I personally wouldn't keep going back and forth.

iwishtofish
01/07/2012, 07:22 AM
Interesting. My pH meter required one dip in each solution. Maybe it might have had more of a computer in it to do the coefficient calculation. I can't think of another reason to do multiple calibrations.


It can take several minutes in each fluid, but once is usually appropriate. Then when done, it is fine to check them in the fluids again. I personally wouldn't keep going back and forth.

Thanks, Jonathan and Randy.

It is such a small amount of calibration fluid. It wouldn't take much contamination to alter it, I imagine. I think I'll stick to one time each, in the future. I didn't wait a few minutes in solution, fearing the air would alter the pH quickly. But I will.

Randy Holmes-Farley
01/07/2012, 07:25 AM
The air won't impact each pouch enough over 10-20 minutes to be a concern. :)

iwishtofish
01/07/2012, 09:08 AM
The air won't impact each pouch enough over 10-20 minutes to be a concern. :)

Ok, good to know!

shaggss
01/07/2012, 09:24 AM
the Profilux takes about 5-6 minutes in each solution to calibrate if that is any reference. I have never noticed any fluctuations and the probe always reads true after.

Squint
01/07/2012, 09:28 AM
If I remember correctly, only the pH 10 calibration solution is really affected by CO2 in the air and even then, it's not that much.

I use calibration solution from mixing powder packets with 100 mL of DI water then store the solution in amber glass jars in the fridge. I would dip the probe directly into the jars and rinse thoroughly with DI water in between. After about a year, I mixed up new solutions and tested the old against the new and the old solutions were still good.

Nowadays, I just pour off a little solution into a 10 mL beaker and discard it after use.

I find the powder form the most economical and having the longest shelf life.

disc1
01/07/2012, 10:39 AM
If I remember correctly, only the pH 10 calibration solution is really affected by CO2 in the air and even then, it's not that much.

I use calibration solution from mixing powder packets with 100 mL of DI water then store the solution in amber glass jars in the fridge. I would dip the probe directly into the jars and rinse thoroughly with DI water in between. After about a year, I mixed up new solutions and tested the old against the new and the old solutions were still good.

Nowadays, I just pour off a little solution into a 10 mL beaker and discard it after use.

I find the powder form the most economical and having the longest shelf life.


Be sure to warm them to room temp before you use them then. Temperature has a significant effect on the pH of the buffer standard.

Squint
01/07/2012, 11:25 AM
Yes, I take them out of the fridge a few hours or even the day before. My pH meter is temperature compensated too but I prefer to measure at room temp.