View Full Version : pinpoint ph ?s
xcdennisx
10/14/2009, 12:07 PM
so i jus recieved my pinpoint ph moniter a couple days ago and i have calibrated it perfectly and its been reading 7.91 and sometimes it mite hit 8.0 after lights have been on for 9hrs but when i tested it wit seachem ph it reads around 8.1. sometimes before the lights turn on its usually around 7.5 - 7.8 ish thats pretty low for my reef tank and all the corals are doing perfectly. so i was wondering if that has anything to do wit the probe being bad?
my other levels:
alk 11.2dkh - 4.0 meq/l salifert
cal 420 salifert
bertoni
10/14/2009, 12:18 PM
[welcome]
The pH monitors seem to be prone to electrical interference, and 7.5 is low enough that I would question the accuracy of the reading. Other than that, the numbers are reasonable. I probably wouldn't worry much, but I might clean the probe and recalibrate with pH 7 and 10 solutions, then watch the daily low again.
pH is generally lowest in the morning before the lights go on and photosynthesis removes carbon dioxide from the water.
dwanner
10/14/2009, 12:56 PM
Not to get off topic, but do you run your PH monitor 24/7 or just use it for spot testing
Randy Holmes-Farley
10/14/2009, 12:57 PM
FWIW, I run mine 24/7 so I can just glance at it as I'm passing by. :)
dwanner
10/14/2009, 01:00 PM
How often do you calibrate it?
Randy Holmes-Farley
10/14/2009, 01:05 PM
When it needs it. :D
If you calibrate it after a week, and it still is basically correct, let it run longer, and longer, and longer until you find it has drifted enough to be a problem. A super accurate lab will calibrate every day, and possibly for each experiment during the day.
My system can run for months with little calibration drift, but I've found that during a power failure, when my probe gets completely submerged in the rising sump, the calibration gets off (not sure why).
Anyway, it is obvious to me when it needs calibration because the readings are different than "normal" for my tank. I also calibrate it any time I am especially concerned with accuracy.
These have more:
Measuring pH with a Meter
http://www.advancedaquarist.com/issues/feb2004/chem.htm
A Comparison of pH Calibration Buffers
http://reefkeeping.com/issues/2005-02/rhf/index.htm
The "How To" Guide to Reef Aquarium Chemistry for Beginners, Part 3: pH
http://reefkeeping.com/issues/2007-05/rhf/index.php
dwanner
10/14/2009, 01:14 PM
Thanks Randy!
Billybeau1
10/14/2009, 02:03 PM
xc, there is nothing wrong with a pH of 7.9
Too many reefers get hung up on this 8.3 thing. I suspect your Pinpoint monitor is correct and, as Bertoni said, no worries.
FWIW, I have not found a titration type pH test kit that can hold a candle to the Pinpoint pH monitor. :)
xcdennisx
10/14/2009, 02:08 PM
been on 24/7
loudell
10/14/2009, 08:59 PM
The pH monitors seem to be prone to electrical interference-<Bertoni>
I gotta tell ya. I cringe when I read this...
NO...they are not prone to electrical interference and if you suspect interference then put the probe back into each of the 2 calibration fluids and see if it reads the values correctly. I'm willing to bet it probably does.
My experience with electrical interference tells me that if someone is using an AC kit and their HO or VHO ballasts are import or perhaps a retro kit this is a potential opportunity for interference. The moment of start up for a lighting product can generate a momentary interference field. Interference is usually NOT demonstrated by a pH reading that is .2 lower than expected. This is usually an indication of "accuracy" that you never had before. Electrical interference is usually apparent by an instability in the reading that will not stop. The amount of instability is directly related to the amount of interference in the AC line. If you see this....try a battery instead of using AC wall power and keep the cable of the probe from contact with the wires from the ballast to the lights.
bertoni
10/14/2009, 11:54 PM
When I put my Oakton meter into a tank with lit fluorescent lights, the reading jumped all over the place. If I turned the lights off, it was fine. The effect was quite repeatable, and the unit didn't have a power line.
loudell
10/15/2009, 08:26 AM
It's difficult for me to comment on an Oakton meter. Frankly one would be difficult to locate in the aquarium hobby; to the best of my knowledge the major aquarium suppliers don't even offer the Oakton pH Meter.
Bertoni do you have an Oakton Meter with a replaceable probe which is somewhat similar to a PINPOINT pH Meter or an Oakton pH pen which almost no one uses??
bertoni
10/15/2009, 11:06 AM
I have an Oakton pHTestr 3+ pen, from LabSafety.com. It's very easy to get.
loudell
10/15/2009, 02:24 PM
Anything is easy to get if you frequent the vendor and you want to buy something. I could be wrong but LabSafety.com isn't a popular provider of equipment for the aquaculture industry besides the fact that pen type equipment can not 24/7 monitor and usually perform poorly.
Just to clarify....electrical interference is almost always indicated as a reading that jumps around every second or so to a different number. My recommendation in this case would be to find out what is producing the interference and repair or replace it. Lights should produce light and not constant AC interference. Your fish/inverts will be living in a significant electrical field. The greatest majority of quality lighting products do not produce interference.
In the case where your color test kit has been telling you for years that your pH is 8.4 and the calibrated meter is saying 7.91 You can check the calibration of the meter by immersing the probe into reliable calibration fluids to verify the meter reading.
But if you see a steady pH reading that you don't like or agree with, one should not immediately dismiss it as "prone to electrical interference". Find out what's going on. Chances are it is NOT electrical interference...
bertoni
10/15/2009, 03:30 PM
Well, it's certainly true that only a minority of people report problems with electrical interference, as far as I can tell, anyway. Still, it's easy to check and does seem to be an issue from time to time.
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