How Do You Test Soil pH With Aquarium Strips?

[ShadyStump]

I picked up some 5 in 1 water quality test strips from the aquarium section at the local pet shop for testing my water and soil pH and other factors. These strips test hardness, carbonate hardness, pH, nitrite and nitrate levels. Aside from my tap water being slightly harder than I thought, but not much more than my half empty rain barrel, no great surprises so far.

Some of my gardenias are producing white leaves, and none of them have flowered. Through toying with them a bit I've concluded it's likely a soil issue, so I want to test the soil with the strips I have, but I'm uncertain of the best way to go about it.

Do I water them and test the runoff?
Set a strip in the soil and test whatever moisture it absorbs?
I'm on a tight budget, so was hoping to avoid getting a different test kit.

 

[Paradox]

I picked up some 5 in 1 water quality test strips from the aquarium section at the local pet shop for testing my water and soil pH and other factors. These strips test hardness, carbonate hardness, pH, nitrite and nitrate levels. Aside from my tap water being slightly harder than I thought, but not much more than my half empty rain barrel, no great surprises so far.

Some of my gardenias are producing white leaves, and none of them have flowered. Through toying with them a bit I've concluded it's likely a soil issue, so I want to test the soil with the strips I have, but I'm uncertain of the best way to go about it.

Do I water them and test the runoff?
Set a strip in the soil and test whatever moisture it absorbs?
I'm on a tight budget, so was hoping to avoid getting a different test kit.

Don't think they will work that way sorry. The pH of the water will effect the results of the runoff or of any moisture in the soil. You won't be able to get accurate results.

If your gardenias need to be more acidic or alkaline, aren't there fertilizers that make the soil whichever way you need it to be?
Aren't they the ones that if you want pink, you feed one fertilizer and another for blue?

 

[Bonsai Nut]

I have never tried using those strips, but I would assume you would simply use distilled water for the soil. Add soil to the water, mix, test the water.

 

[ShadyStump]

Don't think they will work that way sorry. The pH of the water will effect the results of the runoff or of any moisture in the soil. You won't be able to get accurate results.

If your gardenias need to be more acidic or alkaline, aren't there fertilizers that make the soil whichever way you need it to be?
Aren't they the ones that if you want pink, you feed one fertilizer and another for blue?

No, those are hydrangeas.

I tested both my potential water sources on their own first so I'd have baseline to compare if needed, but then I thought that testing the runoff I'd be testing more water than anything else and wasting strips.

I have never tried using those strips, but I would assume you would simply use distilled water for the soil. Add soil to the water, mix, test the water.

This seems like a practical way, but wouldn't I be getting a highly diluted soil reading?

 

[Lorax7]

This seems like a practical way, but wouldn't I be getting a highly diluted soil reading?

It sounds like a better approach than collecting runoff when watering and testing that. If you’re mixing soil into a small volume of distilled water and allowing sufficient contact time for the mixture to reach equilibrium before dipping the test strip, I would expect that to give a pretty decent result. I’ve never done this personally for testing soil (but have used test strips many times back when I used to keep aquarium fish). I would expect soil scientists probably do something very close to this but work a little harder to control sources of error by standardizing the quantity of the soil sample and quantity of distilled water (actually, they probably use distilled DI water).

 

[ShadyStump]

That might be the route I take then. Hopefully I get some clear readings.

 

[Wires_Guy_wires]

Grab a spoon full of soil when it's damp a couple minutes after watering, from the center of the pot, below soil level. Press it on to the paper.
Litmuss paper and lackmuss paper should turn color even with minimal amounts of water. If things get muddy, check the backside of the paper.

The pH balance of water is quite immediate. And pH is always a measurement of water itself. You can't really measure "dissolved/suspended hydrogen" in rock.. Because it's not dissolved.

If your tap water is 8 and your soil is 6, it should read roughly 7.5.
-log10(0.00000001) = 8
-log10(0.0000001) = 6
(-log10(0.00000001)+-log10(0.0000001)) / 2= pH 7.5

Most of those paper strips give a rough indication on whole numbers, but in general you could do the math if you just exchange your pH value minus one for the inverse log 10 value zeroes before the one: pH 6 is 5 zeroes. pH 7 is 6 zeroes. And so on.
Add them up, divide by 2.
If that sounds too mathematical, keep reading. I hate doing math.

If your water is 7 (demineralized water should be 7 at room temp.) and your measurement ends up being 4, your soil is pH 0.1. If you use demineralized water, the calculation is as follows:

((-log10(0.0000001) + -log10(x))/2)= "pH value found" solve for x

now that's some serious math that only some people (not me!) like doing. So go to wolframalpha.com and put that italicized sentence in there, insert your "pH value found" as a number..
It'll give you the answer expressed in a tenth power value. Count the zeroes.

Example: I measure with demin water of pH 7, and the outcome of the paper test is 6.5.
((-log10(0.000001) + -log10(x))/2)=6.5 solve for x
the answer is 10^-7 which is 0.0000001.
count the zeroes. It's pH 6.

I Think our Chemistry, math or computer science dudettes or dudes might be better at explaining this. I'm biochem, I just do whatever the calculator tells me. And yes, I have pre-made excel sheets to help me with these things.

 

[ShadyStump]

Yup, smarter than me.
Thanks! I'll give it a go.

Don't suppose you know how well I should expect this method will work with the other indicators on the strips I have; NO², NO³, etc?

 

[Wires_Guy_wires]

NO2 and NO3 will read 'as is' on your strips because clean water should not contain any noticeable amounts. Then again, I've heard some bad things about the quality of US drinking water. So don't pin me on that.
A TDS or EC value would tell you a lot too. Mainly if your trees are getting any salt stress. But the foliage would show signs too if that's the case.

 

[Ugo]

Hi!

I found this PDF that I follow since 2 years for my PH testing
See file attached

 

[ShadyStump]

Hi!

I found this PDF that I follow since 2 years for my PH testing
See file attached

This is fantastic! Almost everything I might need to know.
Thank you!

 

[Ugo]

No problem my pleasure.

The only thing I do a little bit differently now is putting the dry grinded soil into a tea bag or a coffee filter formed as a pouch.
I let it soak in deionized water for 20 minutes (An hour is a bit too long for me!), I remove the excess of water by pressing gently on the pouch and then press firmly the enveloppe to squeeze the sample water out the substrate.
I did tried this method and compared my results to the complete second method in the document and got the same results 3 times...
but my problem is the reading method as Im not using proper instruments only PH strips so far which I believe I far from being precise...

I dont know whats the next step is in term of analyzing equipement needed to have a proper "home" setup that is good enought to atleast being able to rely on it and apply proper changes after analyzing your tap water Vs Soil.

 

[hampton]

Hi!

I found this PDF that I follow since 2 years for my PH testing
See file attached

Thanks for the reference doc. I exactly what I was looking for.