Which pH meter is better?

[Paph_Person]

I've been wanting to get a good quality pH meter so that I'm aware of the pH of the water I'm watering/fertilising the orchids with and the pH of the media. Which pH meter is better for this task?

GroLine Soil pH Tester - HI981030

or

GroLine Waterproof pH Tester with 0.01 Resolution - HI98118

Thanks.

 

[Arne]

The first and more expensive one seems much better. It has better accuracy and is more straightforward to use.

 

[Ray]

That first one is intended to be stuck down into moist soil to read a pH. I serioujsly doublt it'll be very good in orchid media.

The better choice would be to collect pour-through samples and measure those with a typical liquid immersion probe.

 

[Arne]

That first one is intended to be stuck down into moist soil to read a pH. I serioujsly doublt it'll be very good in orchid media.

The better choice would be to collect pour-through samples and measure those with a typical liquid immersion probe.

Ray is right. The pH electrode must be in contact with liquid water. Otherwise the pH cannot be trusted.

 

[Ray]

I was surprised to learn that the pH of applied solutions has very little impact on the rhizosphere pH. The medium, the plant, and the microbes living in them play a much bigger role in controlling that.

I used to use 25 ppm N Dyna-Grow 7-9-5 in RO water, and the pH was about 4ish, so I metered in their potassium silicate product (ProteKt) to adjust it to 6. Checking the pour-through pH returned a value of 5.5-5.8, so I was happy. One of my metering pumps failed, and for several weeks, the plants only got the fertilizer solution. The pour-through pH was in that same range.

The alkalinity of the water - that is, its resistance to pH change - is more important than the pH. RO has no alkalinity. My tap water here has very low alkalinity, as well, so I don’t even bother testing. The weak concentrations we apply creates such weak acids and bases that they are easily overwhelmed by the other factors.

 

[Califoutdoors]

IME, even the higher end pH meters are a hassle—needing frequent (and costing extra) calibration; in fact many science nerds I know recommend the lengthy calibration process before each and every use, even for $1500+ meters. pH meters are really geared, in my view, for uses that require very specific results, such as in more specialized (scientific) applications where the differences between 6.285 and 6.496 would be important and need to be known.

Growing orchids isn’t really in this realm, IMO. We do need to get ballpark figures, yeah, okay, and the chemical regent tests have worked well for me. I particularly like the easier to read Biopharm kit, available on Amazon for $10. Using their picture, as illustrated below, is easy for me to read.

I’d love to be proven wrong and have someone pipe up about a meter under $150 that’s accurate, calibrates easily, and stays calibrated for weeks, but I haven’t found it yet…!

 

[Arne]

Yes, the pH of pure water does not mean much, if anything. I normally measure the interactions between proteins in solution but always at a set pH in the presence of buffering salts. Once I was asked to measure the interaction between two molecules in pure water at pH 7.4. It never worked because the pH plummeted to around pH 6 once the reaction happened.

 

[Paph_Person]

So what would be the ideal KH of the water we fertilise or water the plants with? Given that I use RO water with negligible KH. @Ray

 

[Ray]

I don’t know that there is an “ideal”, just the lower the better.

 

[JustinR]

I failed to successfully calibrate one of those cheapo pH meters so in the end I just got some pH strips, they are also cheap and easy to use. Just be sure to get the ones with 0.25 grading. My tap water measures 7.0 and collected rainwater 6.25.