What is most accurate PH test
 

Hi Guys,:hello
I am new to this forum but have been growing orchids for a few years now and as I live downunder I have got quite addicted to Aussie Natives.
Since I have been growing orchids I have got to know that PH is pretty important but have not yet found out the most accurate way of testing it,I have bought a cheap PH test probe but to me it seems to read the same all the time so I have my doubts about it being any good.
So the question is, what is the best method of testing.?

PH meter.?
Solution.?
Litmus Paper ?

Whichever one, can you recommend anything as I can order anywhere around the world over the net I presume.

I would appreciate any information you guys can give me and how do you preform the test,do you drench the plant and then test the run off water,which would take a long time with a few hundred plants or do you just test a few random ones to get an average.
Thank you guys in advance.
P.S Pardon my ignorance but what is RO water. :)

A high quality pH meter is easy to use and accurate, but keeping the probe viable involves keeping it wet and calibrating it periodically, which is beyond the effort threshold for many.

Both the wet-chemistry test kits and pH papers are acceptable substitutes. I have a good meter that I use periodically, but rely on paper as the quick check.

Besides, if you can keep your root zone in the 5.5 - 6.5 range, most plants will thrive.

I would recommend checking a few plants individually, to see what's happening, rather than doing a composite.

"RO" is short for reverse osmosis, and mechanical technique of purifying water to almost distilled purity.

Thanks Ray for your valuable information.
I have been on the net and Ph testers seem to go from $10 to about $3000 so that beggars the question what is a good quality one and how much should I spend.
I would appreciate a few other members comments on their experiences with PH meters and what they think of their particular brands, I just don`t want to buy another crap one and if necessary would spend a few bucks to get a reasonable quality one so as to make the test worthwhile.
Regards
Paul

I agree with pretty much everything Ray said, but I think keeping a pH meter calibrated and working properly isn't as hard these days as it used to be, and the answer will be way more accurate.

I used some really expensive and finicky meters in higher level courses in college, but those were extremely sensitive and that was a long time ago. I didn't realize until I started looking for one to use in the greenhouse a few years ago just how far the technology had improved.

I chose a meter designed for field work, which means it's small, tough (tolerates being carried around in a pocket, dropped, etc.), simple to care for, calibrate, and use, and accurate enough for anything I'll need. Mine cost about $100 US; there are several in that price range. The one I chose also has a replaceable electrode; some don't. Unless you're going to take a LOT of readings, it'll be years before you need to worry about that either way.

The three buffer solutions used to calibrate it cost less than $30 US for the set. They do have a shelf life and will have to be replaced periodically even if you haven't used them and have stored them properly.

There is a little bit of lab technique in calibrating, but not much - if you can cook at all, you can do it. Takes under 5 minutes once you know the procedure. There's also a little technique in using it properly, but again - not difficult. Mostly it's just making sure you don't contaminate your buffer solutions or samples before you calibrate or measure, respectively.

Steve

I have a combined pH/EC meter from Hanna which I quite like; I have 3 calibration solutions for pH (2) and EC (1), along with the recommended cleaning and storage solutions. The solutions pretty much cost the same as the meter itself...

Orchids on a Balcony: New Gadget: Combo pH & EC meter

Orchids on a Balcony: Calibrating a Hanna HI 98129

Handily enough, this model has a thermometer built in so it helps to adjust the reading closer to a true reading if the sample is off STP (which they invariably are).

Fairly accurate and fairly cheap liquid pH test can be found in most aquarium/pet stores; just check the expiry date; obviously, you need reasonable colour vision to interpret these; if you are colour blind, you can get testers that incorporate a colorimeter and then read out the pH, but they're usually more expensive than a simple pH meter.

An EC meter is a pretty handy thing - if you're interested in pH, chances are you'll be interested in EC too.

You can pay a lot of money for things that are accurate and precise; things in the ~$100-200 should be both accurate and precise enough for a home user.

If you're at all concerned about accuracy, you *must* calibrate.

whats wrong with something like this for occasional testing ? I mainly want to see if my fertiliser mix is changing PH too drastically.

Neewer New Mini Digital Pen Type PH Meter PH-009 I Multimeter Tester Hydro: Amazon.com: Industrial & Scientific

I would suggest spending 3X as much to get one with an actual brand name on it and 2 point calibration. You will also want calibration solutions.

Hanna Instruments HI 98107 pHep pH Tester, with +/-0.1 Accuracy: Amazon.com: Industrial & Scientific

"you get what you pay for", or as the romans said, Caveat emptor!

I'll say first that I agree with those who recommended buying a higher-priced meter - you do get what you pay for.

I did follow the link to Amazon and read the product description and some of the reviews. My impression is that someone who already has a higher-priced meter and calibration solutions and some basic knowledge of such things could probably get away with using one of these, because they'd know when to be wary of the results they were getting. But someone who didn't might not know if what they were seeing was anywhere near accurate - one instructor had 3 of 25 he ordered that were either dead on arrival, or gave wildly inaccurate readings. That's 12% failure out of the box. (That reviewer actually gave them high marks overall, but his situation was not typical of an orchid grower.)

Steve

I've been using this 4 in1 Soil Tester for Moisture, PH, Temperature, and Sunlight....I know there is a lot of Tester out there much better and much more expensive than this one....but this worked for me just fine with just $30....

This one?
Amazon.com: Luster Leaf 1818 Rapitest Mini 4-in-1 Soil Tester: Patio, Lawn & Garden

Have you ever tested it with solutions of known pH to see if it actually works?

Thank you Guys for you information,the consensus seems to be a Hanna around about 35bucks ,I was thinking to get anything decent I would have to spend a fair bit more but if you guys think they will do the job,that suits me,I can buy a few more plants instead.:):rofl:

Did anyone have experience with RePotMe test-stripes? they seem to have convenient range (3.5-7.5 pH) but a description on their website says they had RO water test give 4.5 pH, which makes me question its accuracy. Is it at all possible, that RO water out of a can could be so acidic?

Although the pH of absolutely pure water should be 7.0, really pure water that's left open to the air will wind up with a pH of about 5.65 because it will absorb ("equilibrate with") gases from the air that are acid anhydrides. Mainly CO2, but trace amount of other things like NO2, SO3, etc.

(5.65 is a theoretical value I saw somewhere, based on 335 ppm CO2 in the atmosphere if I remember right, but it's pretty close to what I see when I do the experiment.)

That said, I've used indicator papers before - my wife was a chemistry teacher for years so we have lots of Hydrion paper lying around - but I don't consider them to be accurate for more than a general idea (more or less neutral, acid, alkaline, very acid, very alkaline).

Steve

Thanks, Steve - well, 5.45 is different from 4.5, I guess :)

These strips? They are 4.5-7.5.
PH Test Strip Kit - 15 feet

I have that product though I bought it from Amazon. This is a good pH test paper. RO water cannot be used for testing the accuracy of a pH paper since even trace amounts of other materials in the water can cause the pH to vary from the theoretical value of 7.0 by as much as +- 2pH units.

These pHydrion brand, 4.5-7.5 pH papers can be used to determine the pH of a solution between pH 5 and pH 7 to about +-0.5 pH unit which is good enough for a quick check on your fertilizer solution. If you want better then you need to spend about $40 for a pH meter with 2 point calibration and also buy calibration solutions at 2 different pH values.