Are you sure about that?
While true, the world usually runs on 0-14. No Pocket pH tester needs to go outside that, nor would one be accurate for long testing those extremes.
SPECIFICATIONS
RANGE
-2.0 to 16.0 pH (pH 55)
-2.00 to 16.00 pH (pH 56)
-5.0 to 60.0°C / 23.0 to 140.0°F
RESOLUTION
0.1 pH (pH 55)
0.01 pH (pH 56)
0.1°C / 0.1°F
ACCURACY (@25°C)
±0.1 pH (pH 55)
±0.05 pH (pH 56)
±0.5°C / ±1°F
I have used this exact instrument for the previous 2 years. In my experience, the probe only lasts 1 season before it no longer holds calibration. I threw the first one away after year 1, and I threw the 2nd one away after year 2 (last year). I've already ordered another one for this year. The probe and a year's worth of standard calibration solution costs me about $25. I seem to recall spending about $25 per year in phenol red, so I guess it's break-even for me!
Jay,
I agree they're not necessarily more cost effective. But for me it's not all that much to pay for a test that works. I have color-blindness that make ph above 7.5 almost impossible to discern. Now that 2 point self calibrating systems are under $15 and even considering the $20 for a years worth of calibration it's just worth it for me. Also there's a big benefit that the meters measure accurately over 8.2 which the drop test can't do.
Thanks for your comment and I hope that helps clarify.
Chris
You test pH a lot Jay! Good on you!
The pH meters incapable of a two point calibration are not worth having. Any that can, should be able to calibrate to a 4&7, or 7&10 two point Cal sequence. All of them should be stored wet, and frequently calibrated for optimum results.
pH can go below 0 and above 14. For concentrated solutions of sodium hydroxide, the concentration of OH- can exceed 1 molar. So, the pH can go as high as 15.75. Remember that the standard pH range of 0 to 14 that everyone is familiar with is what is defined by water's equilibrium constant (1x10^-14) and is a measure of the ratio of the thermodynamic activities (denoted "a") of dihydrogen oxide (H2O) to the product of hydronium activity (H+) and hydroxide activity (OH-). Activity is proportional to concentration. When concentrations exceed 1 molar, then the pH can go above 14 or below 0. Another example is muriatic acid - at 20 Baume the concentration of HCl is 34.45% which makes the hydronium (H+) concentration greater than 1M. This means the pH is less than 0 or approximately -1.
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Agreed. Stick one of those pocket testers in 27M NaOH (highest concentration possible at room temperature) and I doubt very much it would last more than a minute or two....
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For my pool, pH is the only property that changes on a daily/weekly basis. Between the SWG and several water features, pH is always rising. This causes me to test pH quite frequently. The other properties are rock-solid, so I test for them infrequently.
I work to keep my alkalinity down, but pH is still constantly rising. I keep thinking about converting to the borate buffer, but I'm concerned about the effects on my dogs (who drink lots of pool water).