electronic soil ph tester

matthew18(5)February 14, 2010

I was in home depot the other day and saw an electronic soil ph tester. Has anyone had any experience with a product like this? Are they accurate, reliable?

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ericwi

Some pet stores sell an "aquarium water pH kit" that can be used to test soil pH. The range is limited, I think it covers 6 to 8. You take a small soil sample, maybe a teaspoon of dirt, and mix it with distilled water to make a slurry. Then you filter the slurry with a coffee filter, and test the filtrate for pH. The nice thing about indicator solutions is that they don't have to be calibrated. Won't work if you are colorblind.

    Bookmark   February 14, 2010 at 4:23PM
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matthew18(5)

well just to clarify..its "electric" and its made by Burpee. sorry for any confusion

    Bookmark   February 14, 2010 at 7:06PM
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ericwi

I'm not confused, I was trying to be helpful. There have been many discussions of metal pH probes, the kind that sell for 20 dollars or less. Some folks have gotten good results, and others find them useless. There is general consensus that this type of meter can't be calibrated using a standard solution of known pH. Since these units can't be calibrated, its difficult to know if they are accurate, or not. If you price pH meters from a scientific supply house, you will find them selling for 50 to 500 dollars. All of these units can be calibrated, using standard solutions. However, there is a disadvantage to buying one of these. They are fragile, the glass bulb is very thin. Also, they are subject to contamination. Get the bulb dirty, and you might not be able to get it clean and working again. You have to keep the bulb wet, in storage solution, when the unit is not in use. And, finally, these units have a limited life. I have a Hanna Instruments pH meter that is three years old. I doubt that it will last much longer. On the other hand, testing for pH using an indicator dye solution is inexpensive, accurate to about 0.5 pH unit, and there is no need for calibration. An 8 dollar kit will contain enough indicator solution for about 100 tests. Indicator dye is a low tech method of pH analysis. It won't replace the wet bulb type meter for lab use. But it works well for growing blueberries. We have alkaline soil, high in calcium and magnesium. I have to use both granulated sulfur, and also diluted vinegar, to lower soil pH, and keep the blueberry shrubs healthy and green. I have to test soil pH every spring, guessing just won't cut it. Adding too much acid will kill a shrub faster than doing nothing, so there is no substitute for pH testing. From personal experience I know that the type of indicator dye used to test aquarium pH works well for soil testing. The results that I am seeing agree with the results that I get with a calibrated pH meter, every time.

    Bookmark   February 14, 2010 at 9:27PM
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gator_rider2(z8 Ga.)

Champ by Hanna is good ph meter. I've had mind for over 20 years still works on same batteries I go 4 years never use tester in summer of 2006 last time used meter I keep here in computer desk just check battery still good.

    Bookmark   February 14, 2010 at 11:18PM
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matthew18(5)

ericwi, I didnt mean to imply that you were confused. I just want to make sure i was givig an accurate description. thanks for the additional detail

    Bookmark   February 16, 2010 at 7:37PM
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ericwi

Well, I could be confused, it happens now and then. The metal probe type pH testers are a conundrum to me. I can readily see how a double prong probe could be used to measure soil resistance(electrical), and how soil resistance might correlate to soil moisture. But I don't see the physical principle behind single metal probe soil pH testers. I have never seen a good explanation for how these work, the operating principle. This type of pH tester has been discussed before, and others have stated that "you can't calibrate this unit with an aqueous solution of known pH, because the unit only works in soil." My understanding is that pH is a measurement of hydrogen ion concentration in solution, usually an aqueous solution. How can a pH proble work in soil, but not in an aqueous solution?

    Bookmark   February 16, 2010 at 11:00PM
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tantanman(z9Tx)

Eric:

Thank you. My sentiments exactly. The economy models you cant test and trust. The good ones fragile high cost with short electrode life. So easily contaminated.

Larry, retired chemist.

    Bookmark   February 26, 2010 at 1:07PM
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catlady4444(7)

Hello,
I just came to the same conclusion the hard way. I've owned several inexpensive pH meters, none of which worked. This week I bought an electronic one (Rapitest, the company I now love to hate) and it malfunctioned on the 2nd use. Brought it to the store where they opened another one for me, which also malfunctioned (froze "on" like the other one, then won't turn on at all.) In a frenzy, I did some research and found this article (http://www.joe.org/joe/2001august/tt3.php) Now I am wondering if there are pH test kits that are better than any others, more precise measurements, etc.

The one I have is Rapitest (ugh!) and measures in 0.5 increments. Are there any other choices that anyone has had luck with?

Thanks,

Ann

    Bookmark   April 20, 2010 at 9:46PM
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ericwi

There are several dye indicator solutions that can be used to test pH. One for sale in pet stores is used to test aquarium water, over pH range 6.0 to 7.6. The kit comes with a color card, so you can estimate the pH in the mid-range. There are other indicators available, like bromocresol-purple, which is yellow at 5.2, & purple at 6.8. Bromocresol-green is yellow at 3.8, and blue at 5.4. To use these, you take a small soil sample, and cover it with distilled water. After a 20 minute soak, the solution can be filtered with a paper filter & funnel, and the filtrate is ready for testing. A bottle of dye indicator might cost 2 dollars, and it will do about 100 tests.

    Bookmark   April 20, 2010 at 10:34PM
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franktank232(z5 WI)

I think they sell those kits for pools or hot tubs too... I might try one.

    Bookmark   April 20, 2010 at 11:15PM
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mr.ed

I have one. I tested it in vinegar and it seems accurate enough for what I do, but the soil must be soaking wet.... and the probes must be wiped off before use. Because it needs to be so wet, I use rain or pond water as our water is a PH of about7 and would pollute the results.

Best of luck

BTW; the Champ by Hanna, recommended by Gator Rider is superior to the Burpee or itÂs clones.

    Bookmark   April 20, 2010 at 11:57PM
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catlady4444(7)

If it's not meant to test soil, I don't know that I'd trust it when using to test water soaked soil, rain or tap water or distilled or any other. The water dilutes what's going on in the soil and I don't understand why it would be accurate (unless it's meant to be used that way, like Rapitest.)
Eric, do you know of any that are specifically for soil?

Thanks,

Ann

    Bookmark   April 21, 2010 at 7:02AM
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catlady4444(7)

This is disturbing, but the guy's logic is hard to dispute. Sigh....

http://www.waynesthisandthat.com/soiltest.htm

Ann

    Bookmark   April 21, 2010 at 7:15AM
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ericwi

When testing soil pH, one method, used by soil science labs, is to mix the soil sample with distilled water, and then filter the soil & water mixture. The result, the filtrate, is what gets tested for pH. The test can be done with a calibrated pH meter, or it can be done with dye indicators. For really accurate results, you need a pH meter, because these units can be calibrated so they will indicate plus or minus 0.01 pH unit. So if you need to know that your soil is at 6.45, because 6.46 is too high, then a pH meter is the method of choice. The same filtrate described above can be tested with a dye indicator, and the result might be 6.4, plus or minus 0.2 pH unit. That means the sample has pH in the range 6.2 to 6.6, and this is close enough for some gardeners.

    Bookmark   April 21, 2010 at 10:15AM
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mr.ed

catlady4444 soil cannot be tested unless it is moist, even the best units require moisture. I test after a rainfall because that is the daily PH the plant is subjected to. Even a high PH water only affects the test in the slightest degree. They need moisture for conductivity, and without itÂÂÂ..well, this may be why your meter gave false or no readings.

    Bookmark   April 21, 2010 at 2:36PM
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fruitnut Z7 4500ft SW TX

I've got some pH indicator strips. They read 4.0 to 7.0 and seem pretty good. They are marked ColorpHast from SanitationTools.com. 100 strips are $19.57. I stick them in moist soil and leave 10-15 minutes. Readings are repeatable. They work in water also which is very helpful adjusting well water pH with sulfuric acid.

My Rapitest electronic meter reads all over the place. Properly cleaning and shining the metal probe is supposed to be the key. And the soil has to be soaking wet.

I have much more confidence in the strips and they are easy to read.

    Bookmark   April 21, 2010 at 3:22PM
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