Calibrating Digital PH Meter

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Arizonarob

Arizonarob

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Mar 25, 2018
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So I picked up the digital PH meter from TFTestKits.net to do quick testing this season, and the thing needs to be calibrated. Problem is, it’s needing a 250ml glass beaker to do it. Now I don’t know about the rest of you, (except for @JoyfulNoise who probably drinks coffee out of them in the morning) but I don’t keep those things just laying around. Any easier way to calibrate the thing?? :scratch:
 
I use a plastic container that spices came in. Polyethylene. I just cut off the top, the diameter is perfect for the small size of the probe. I use power buffers from Hach. Just mix with distilled water.
 
Wait, you don't have any red Solo cups lying around from the last beer pong tournament :cheers:????

(And YES, I do own several glass beakers of various metric volumes...50, 125, 250 and 500mL....now excuse while I go cook up something explosive....:coffee:)
 
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I calibrate my PH Meters using pH 7 standard solution. You can find it on Amazon and other places on the net.
 
ajw22 said:
I calibrate my PH Meters using pH 7 standard solution. You can find it on Amazon and other places on the net.
Click to expand...

For the cheap meters with single point calibration, pH7 is about where it's at. That's the zero point of the sensor, so by adjusting there you adjust the entire offset. You can use a pH4 to check the slope of the sensor but there's nothing you can do about it should it be off. Even with the slope being off, calibrated at 7 it'll still be more precise than phenol red and probably just about as accurate.

I've had a cheap one for a while now (got it free with a TDS meter). The biggest issue I've found with the cheap meters is not having a sealed cap to store the electrode wet. No matter what I put in the cap, it always dried out and that led to difficulty calibrating, drift and unreliable readings. It's a toy, but I keep it around to play with just to see how it performs.

A couple of months ago I took to "storing" it by standing it in a beaker with 30ml of electrode storage solution sitting on the shelf. As it slowly evaporates I top it back up to 30ml with DI water every couple of days when I walk past. Since then the cheap meter has been a lot more usable. Still requires calibration more often compared to the good one, but at least the results are now consistent. If I'm after a quick lo-res check (is it between 7.4 & 7.7) I'll use it in preference to rinsing and storing the better unit.

I periodically buy 500ml bottles of pH 4 & pH 7 calibration solution. Recently I found a hydroponics supplier around the corner and they have similar stuff but at 1/2 the price (with the caveat it doesn't come with a calibration certificate). Shelf life on that is 12 months, then 6 when opened, but in reality as long as it's looked after (don't dip in the bottle, don't pour back in the bottle and keep it inside with the cap on and away from sunlight) it seems to last a lot longer (ie my current stuff reads the same as the stuff I have that is 2 years old).

My good meter has a much narrower probe than the cheapie, so I can calibrate that in a couple of 30ml shot glasses. I use the left from that in a small beaker to calibrate the cheap one.

It's more effort than using phenol red, but then FAS-DPD is more effort than the dpd tablet.
 
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I use a shot glass or a 50ml beaker for my salt meter. Theres less wastage with the shot glass.
 

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I have problems with the red and purple color shades on the phenol red test so I used the cheap pocket probes- calibration became too much of a pain and luckily I trained myself to get better using the calibrated meters. I check myself every now and then with the calibrated meter and I'm usually right on.

Chris
 
Arizonarob said:
Allen, is This the one you’re referring to? And how often are you calibrating your meter?
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That calibrating solution should work although I have not used it.

Well I have not needed to check my pool pH in about 6 months. If you read my PH Meters thread you saw I have two meters. I calibrated them when one did not agree with the other. Seemed about every 2 weeks or so one might drift .1 off. .1 drift is not a big deal. pH 7.8 is as good as 7.7 and more accurate then phenol red tests. I found they always drifted higher.

My municipal tap water is always pH 7.6 and I would use that as an informal accuracy test when I cleaned the meters.

The yellow ATC meter is prone to being left on. When I would find it was left on for a few days it would need calibration and could be off by a few tenths.

So I calibrated as necessary and had my own informal quality control checks on the meter accuracy and no fixed schedule.

I will see soon if my meters are usable after a 6 month hibernation or if they are good for only one season.
 
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This is a good meter with 3-point calibration and a storage cap that has a wetted sponge to keep the tip moist. It also has a replaceable tip so you can keep the guts of the meter and only change tips when they go bad.

Of course you could by 20 years worth of phenol red indicator for the cost of one of these :unsure:

HM Digital Waterproof pH Meter, PH-200
 
JoyfulNoise said:
This is a good meter with 3-point calibration and a storage cap that has a wetted sponge to keep the tip moist. It also has a replaceable tip so you can keep the guts of the meter and only change tips when they go bad.

Of course you could by 20 years worth of phenol red indicator for the cost of one of these :unsure:

HM Digital Waterproof pH Meter, PH-200
Click to expand...

I think that meter is overkill for pool testing. The Waterproof Pocket pH Tester with 0.1 Resolution - pHep® - HI98107 - Hanna Instruments is half the price and a full new Hanna meter costs less then a HM replacement tip. It has 3 point calibration if you want to spend money on 3 sets of calibration solutions. We don’t need 2 decimal point accuracy.

And it costs less then 10 years worth of phenol red indicator! A real bargain!!
 
Any digital pH meter is unnecessary for pool water. Phenol red gives fine enough accuracy for anything that needs to be calculated. I understand people might have trouble seeing the color gradations but that can be overcome (ask a family member to pick a color....my kids are great at it). But, if one must have a meter, then you’re probably just better off buying cheap ones and throwing them away at the end of the season.

For those with acidic water conditions that don’t like the yellow/orange color of phenol red, you can use bromothymol blue indicator (6.0 - 7.6, yellow/green/blue). It used a lot in aquaria and hydroponic work.
 
I want to jump in with a calibration and testing question. How does water temp play into calibration and then testing. Meaning if you calibrated at a room temp of say 70-78 degrees what is the range of pool water that can be tested and considered valid?
 
jimim said:
I want to jump in with a calibration and testing question. How does water temp play into calibration and then testing. Meaning if you calibrated at a room temp of say 70-78 degrees what is the range of pool water that can be tested and considered valid?
Click to expand...

For our purposes pH is stable across the temperatures we deal with in a pool.

For further reading The Effects of Temperature on the pH of Water
 

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