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RE: Aquatic Plants Digest V2 #302
I've got a Sandpoint pH controller on my tank, and after much too long a
delay, I'm finally getting around to cleaning and re-calibrating my probe.
Unfortunately, I can't remember that very safe place I decided to put the
Sandpoint instructions :-), and I can't seem to find a working phone number
for Sandpoint (are they out of business?), so I'm not sure of the proper
method to recalibrate the probe.
What I've done, based on memory and guesswork, is to clean the probe, put
it in the 7.0 standard, and turn the calibration screw until the meter
reads 7.0. I then rinsed the probe, inserted it into the 10.0 standard,
and adjusted the slope screw until the meter read 10.0. This seemed to go
fairly smoothly, but I can't help wondering if I should have gone the other
direction (set to 10, slope to 7), particularly since the range I'm
interested in is 6.0 - 6.5, or whether I'm forgetting a step or two here.
If anyone can enlighten me as to the proper procedure, I'd be much obliged.
Greetings,
Yes you have done the calibration correctly. The reference electrode in a pH probe is
referenced to 7pH. When the probe is placed into a solution of 7 pH, the output of the
probe is 0mV. The electronics have then to be calibrated for zero. I cannot exactly
remember what the change in output of the sensor with pH but at 10 pH, the sensor is
reading a negative voltage. Setting the slope is then carried out at this point.
Cleaning pH probes.
It has been suggested to me be a manufacturer of pH probes in Aussie, that an effective
method for cleaning pH probes is to use pH neutral hair conditioner and a non abrasive
cloth, and then to soak the electrode in either a pH buffer solution close to the pH you
wish to measure or a 0.1 molar strength KOH solution or to use distiller water.
To regouvenate older probes, soaking them for 12 hours in the solution to be tested,
ie to aclimatise them, will help to reduce the insidence of eroneous readings.
I have been doing investigation into pH electrodes now for the last 12 months in search
for a suitable probe for use in aquaria (freshwater), and found some very interesting
problems associated with them as far as longevity is concerned. Unfortuneately all
my info is at home, while I write this message to you at work. So I shall have to post
what I have found later.
I have designed a microprocessor based pH monitor for my plant tank (750l), which is
currently monitoring my 50 litre plant tank, as a test. It currently data logs to a PC
and I can graph the pH swings over weeks. You can see the water changes quite easily,
as well as when the lights go on and off and when I feed the fish.
Marque Crozman APD - ANGFA(NSW) <><
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