Great way to test out your pH probe/monitor results - The Planted Tank Forum
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post #1 of 3 (permalink) Old 03-05-2005, 01:50 AM Thread Starter
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Great way to test out your pH probe/monitor results

After the last several weeks of stressing over varying pH readings between testers (i.e. probe vs. liquid tests), I first off figured out why i was having a problem... 2nd of all I tested it out on some given pH solutions (other than the calibration packages that you calibrate the monitor with).

In the past I had always used the packets from American Marine Inc (manufacturer of my pH probe), and never seemed to disagree with the results of pH readings. Last month I had purchased and began using the Coralife 7.0 and 4.0 pH calibration solutions... and to my dismay turned out to be the mistake. For some reason the 7.0 solution was reading at 6.6 (found this out later during my tests). So, when trying to calibrate the monitor to 7.0 it was thus giving a false reading of .4 pH. For some reason the 4.0 was reading perfectly though. So, I threw that stuff out, and went back to the American Marine Inc solutions.

After calibrating the probe/monitor with the American Marine Inc solution, I was still a little doubtful as to the readings. So, I put together 2 control tests. 1) neutral buffered 5g bucket of tap water, and 2) filled a 2nd bucket of tap water (tap water is ~ 2 KH so not high) and added enough baking soda to bring it to 8.2 pH (maximum pH with the use of carbonates). I then tested the calibrated pH probe in the 2 solutions and got the expected readings... which to my belief means that it is now 100% accurate, since I have calibrated it with a 4.0 solution, 2 7.0 solutions, and a 8.2 solution and got the expected results. I also tested all this with a liquid tester and got ~ the same results (within .1 or less of each)

Now, I went back to the other calibration fluid, calibrated my pH probe/monitor to it, and went back and tested with all the same solutions, and go figure was about .4 - .5 off from each (both 7.0 solutions read at 6.6, and the 8.2 solution read at 7.7). Thus proving that the 7.0 Coralife calibration solution/fluid was not reading correctly.

So I can go back to just trusting my pH probe rather being so doubtful all the time. Moral of the story... don't try skimping on the $ with calibration fluids, and make sure you test your pH probe to some other solutions after calibrating it. I had been thinking my pH was 6.6 in my planted tank (thus having about 25ppm co2) when I was actually at 7.0 pH with 12ppm co2... big difference in results.

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post #2 of 3 (permalink) Old 03-05-2005, 08:58 AM
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Great to hear you finally got to the bottom of this problem!

I found this just the other day when looking at calibration solutions... Comparisons

I guess it's best to stick with reputable makes that are tried and tested by many others!

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post #3 of 3 (permalink) Old 03-05-2005, 11:41 AM
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Very nice link from Stu - an interesting read!

Also have a look at this thread... - Motifone was having the exact same problem with Coralife calibration solutions. Further into the Thread read the comments from Milwaukee tech support regarding same...

Thankfully I had read this thread the other day before I bought my new batch of calibration solutions - because Big Al had the Coralife ones on sale - I coulda been stuck with some very expensive toilet fodder as well...

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