Does anyone have suggestions for a good quality PH meter.......Digital or
analog meter, doesn't matter, provided that it is reliable. The one I got
from my local garden center reads 7 for all areas of my garden. I knew it
was a dud when I placed it in pure lime juice, and it still read a PH of 7.
Any ideas would be greatly appreciated.
All the meters that I know work on the same principle - bascially, they read
the electric potential between two parts (metals) of the shaft, or the
electric potential between two side-by-side different-metal shafts, using
Ph 7 is no potential (zero voltage).
It's a very small potential, and there has to be enough of a current flow in
the meter bridge to register.
The oxide on the metal and/or the lack of fluid in the path both reduce
the flow available for the meter. However, too damp soil or a dirty
insulator, and the path is primarily in the fluid/dirt on the insulator
instead of primarily through the meter.
First, you need to wipe the stem clean before using, but not damage it or
smear metal or dirt across the insulator separating the two metals. Wipe off
the crud at the insulator with a wet kleenex, wipe dry, and then use a
dollar bill or brown paper toweling to remove the oxides right before
Turn around the shaft to wipe it, rather than wipe along the shaft.
Second, the soil needs to be damp but not wet. The meters don't read mud
City tap water has a ph around 8.4- 8.7, depending on the time of year,
so if you put it in the soil with tap water, you can read higher ph than the
soil. I read a day or so after a rain (NOT sprinklered), or I put a few
drops of distilled water in the soil and mix it up before reading.
Third, if you don't get a reading, the soil is too dry, too wet, the probe
is dirty, or the meter is broken..
So wipe it per above and dampen the soil with distilled water, and if it
still won't read, then test it by wrapping it with a damp napkin sprinkled
with baking soda (ph about 9-10) - and then clean it and test it again using
a napkin dampened with vinegar, soft drink, or beer (ph 3-4).
If it doesn't read a damp napkin, take it back to the store with a damp
soil sample, and get one that works on the sample.
Interesting site. How is it relevant to the original question? Are there
any glass electrode portable systems suitable for use in the garden? How
much do they cost? For garden or agricultural purposes why would you need
accuracy down to decimal points of a pH unit?
Although the site is somewhat user hostile, there are explanations of pH
strips and pH papers/indicators. Plus, I see no reason a 'pen' or probe
type device couldn't be used in a soil slurry or other very wet, soil
derived solutions. And it IS likely, especially given the difficulty of
soil testing as provided in the other ratehr good link, that decimal
point accuracy means little - but if it comes along with an inexpensive,
convenient, long shelf life piece of test equipment, I see no problem
with that. Some folks may find a way to use a pen or probe for multiple
duty - soil, tropical fish, pond, etc.
Bottom line for me - I have two portable probe-type "garden-style" ph
meters - neither works in water (tried them for fish tank, tap water, boiler
water, etc.), but both work just fine in moist mediums.
Why is that? I believe the reason the portable non-battery probes don't
work well in fluids is for the same reason they don't work with well with a
dirty probe -
Using a dirty probe defeats the insulator because it provides a current
path across the insulator, just as immersing the probe in a conducting fluid
defeats the insulator because it also provides a path across the insulator.
As I said, the portable types (without batteries) need a certain current
flow through the meter to make the meter move, and that flow is from the
potential difference in the two measuring elements, flow caused by the
imbalance in the hydrogen and hydroxyl in the measured medium (we are trying
to measure the "free" hydrogen).
The probe materials each gather their hydogen or hydroxyl, and the meter
reads the draining of those two pools of different charges through the meter
Water is hydrogen hydroxyl ( H+ OH-, or more commonly H20). It is a
Having the probe insulator immersed in fluid water will have the same
effect on the insulator and circuit as having a dirty probe insulator -
And it IS likely, especially given the difficulty of
Care to drop me a line and explain why do you think so?
There is one problem - glass electrode (or more precisely the bubble at
the end) is made of extremally thin glass, thus it is very fragile. But
that's not a problem you can't overcome with good engineering. Note,
that due to the way pH electrodes are made they will age - at best they
can be used for about a year (gell type). Flowing electrodes can be
used much longer, but they are difficult to maintain.
See my other reply - one decimal digit is important. I wonder if the
difference between 6.5 and 7.5 won't be large enough for the hydrangea
to change flower color.
Yes - and soil electrode (while best for soil pH measurements) can be
used for such applications as well. But it will be probably overkill,
IMHO pH stripes will do in all these cases.
I just found it tricky to find links to pH strips and info thereon and
generally 'search' for specific subjects. It's there I'm sure - but some
of it felt 'buried'. I've seen much worse. Generally, folks patience
with a website goes down exponentially with the number of pages they
must click thru.
Partially only, but it is a good introduction to pH measurements. IMHO
it is better to know a little bit too much, then not enough :)
Google for pHC2051 made by Radiometer - that's the electrode. pH meter
is a separate thing, there are battery field units available from many
One decimal point my be important, as soil pH changes in rather small
range - and the difference between 6.5 and 7.5 is rather important,
while every soil in this range will be measured as just 7 (perfectly
neutral) without any decimal digits. But IMHO you don't need the pH
meter in a garden, for most cases pH stripes will be enough. Especially
if you will use not universal ones (0-14) but some for smaller range.
See examples at http://www.indigo.com/science-supplies/ph-paper.html -
there are papers for range 5-9, while these described on the page are
targeted at body fluids, I am more then sure that you will find similar
ones for soil measurements.
AFAIK there aint no such animal except in a laboratory. The little portable
probe ones rely on the moisture in the soil to get a reading and since that
is not constant they are unreliable. I recommend a dye indicator test kit.
These are cheap, easy to use and reliable. IIRC lime juice is about pH 3 or
4 so take it back for a refund.
The soil type pH meters are not accurate in most situations. You should get a
real pH meter (Daigger has good prices) or some soil test kits. If you get a pH
meter, you need a calibration standard too. You can mix your soil with about 2x
amount of water thouroughly, let the soil settle, and measure the pH of the
real pH meter (Daigger has good prices) or some soil test kits. If you get a pH
meter, you need a calibration standard too.
Calibration procedure in details:
As described here:
Note that final result of measurement IS procedure dependent.
Thanks to all for your responses to my PH question. I am truly a lot better
educated now. My inclination is tending towards the color indicator using a
sample of the soil with a measured amount of water, and then comparing the
color to that of a chart. I was looking at the meter option for the
convenience of being able to test multiple areas quickly.
I know that my gardens require an application of lime, and I want to be able
to do it accurately and know when I've added enough without having to guess.
Yes, I know the standard pHydrion roll you're likely to get if you don't
specify anything is fairly wide range; however,
they also make very nice shortrange papers, e.g., pH 3.0 - 7.5,
pH 6.0-8.0, 6.5-9.5: hundreds of tests for under $10.
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