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Re: pH monitor

Chuck wrote:

To: "plants" <Aquatic-Plants at actwin_com> 
Subject: pH Monitor 
From: "Chuck Gadd" <cgadd at cfxc_com> 
Date: Mon, 22 Jan 2001 00:39:14 -0700 



Ok, just purchased a used pH monitor.  I have no idea how old the probe is, 
so I
won't be surprised or dissapointed if I need to replace it.  I'm going to get
some calibration fluids this week.   Right now, I've got the probe in my 
sump tank, and the meter reading seems to be jumping thru a range of values
from 6.6 to 6.8.   I know that the values aren't really usable until I
calibrate, but is the jumping values a sign that the probe is toast?  I 
did notice that today when doing a water change, the probe reading climbed, as
I'd expect since I add new water into the sump.     And by tonight, the values
were back down to the 6.6-6.8 range, so it seems to be functioning somewhat.

What calibration fluids do I need?  I see that they sell a 4, 7, and 10.  
do I need to be concerned about adding grounding probe?  I seem to recall 
mentioning that stray voltage from pumps and/or light ballasts could effect 

And if I do need to replace the probe, any recommendations on where to find
the best price?

Chuck Gadd

I reply:
You didn't mention the brand, so I'll guess you have an American Marine unit 
(they sell the most). They are good units. Your unit will have 2 point 
calibration. You must use a pH 7 solution can use either pH 4 or pH 10 calib. 
solution for the other. 

Any of the MO houses has the replacement probes at around the same price: 
$45-$50. I wouldn't buy a replacement until you calibrate the meter. When you 
calibrate a meter, you are calibrating it to the operating characteristics of 
the probe, really. A new probe is needed when the meter fails to hold a 
calibration and you get wildly fluctuating readings on the meter. It sounds 
like your readings are pretty stable, so your probe sounds okay. When a probe 
is wasted I usually see at least a .5 pH variance between high and low 
readings if it fluctuates quickly, or a stable but ridiculously high or low 
reading totally inconsistent with a test kit reading. 

Set the probe in your sump with all your equipment running see what your 
readings are, then turn all the pumps, etc in the tank off and see if the 
readings stay consistent. This will tell you if you have any electrical 
interference. Otherwise, you could locate the probe in the tank itself. None 
of my tanks are grounded. No electrical interference issues

If you don't have instructions for proper calibration procedure, email me off 
list and I'll help you. It is important to do it the right way to get 
accurate readings. I do this every couple months to my controllers/monitors.