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API Tests vs. Meter

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I just tested water with API Kit (let's just talk Ph) - tank water with API kit was 7.2... With meter it read 8.2.

Then tested RO water I have access to. API kit was 7.6 (ph) and the meter was 8.6.

What am I to believe? Do we think the meter is a point out of calibration and how bad API to use as a gauge. Do I but water from store? What do I want to buy? Can I just use bottled water?

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I have found my API pH test shows a drastically different pH from my pH meter. Its usually .5 off or more, I found out t he hard way there is drastic difference in a TB tank between pH 6.8 and 6.2 To acurately gauge you would want to get a pH buffer set 4,7,11

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Have you actually calibrated your meter? Also, what type is it, perhaps someone knows how accurate & precise that model is, etc.

Just based on your limited test, it looks like it is a point off.


Yes, digital meters require periodic recalibration and the probes wear out with time. Have you stored it wet in a storage solution or a pH 7 fluid? 

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My money is on the API test and the meter needs either re-calibration or a new probe.  


One thing the manufacturers don't tell you is that you MUST store the meter in a KCl solution between uses.  If you don't the probe will be ruined.  I don't know the specifics, but if stored dry or even in fairly pure (tap) water it will loose it's ability to provide the proper signal.  Additionally they calibration is only good for a couple weeks -- even on the best meters. Finally - if the meter has only a single point calibration adjustment it's a P.O.S.  You just must have two point calibration to get the proper slope which will change over time with a probe as it ages.  CHEAP pH meters use a single point (0Mv) @ 7.01 and that's good for a brand new probe - but unless your fastidious about your care of the probe the slope will be way out of wack in a few months.  In the industry - the $30 pH probes are referred to as "disposable".  There is a good reason for that.  

Finally, you can tell an adequate meter because it will use a BNC connection and have a probe that can be replaced periodically -- that's because the probes do need to be replaced periodically.  


1. store probe in KCl

2. Calibrate every couple weeks

3. Two point calibration 

4. replace the probe if it's slow to react or settle on a reading. 

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