Testing PH runoff in soil

Hi, im going to test my runoff's PH but im a bit uncertain exactly the right way to do this. I have well water so Im using RO and my RO water after its been filtered comes out between 5.5-5.7. How can i determine the PH of the soil using this water?

Testing the runoff isn't going to tell you that much about the soil. It will tell you more about what you're draining to waste then the soil.

So, basically you have two options.

1. Send it to a lab to get it tested. Most will cost about $40 or so. QAL.us costs $32.50, so with shipping, $40. This has more benefits than just giving you soil pH. You will also learn about you're nutrient concentrations in the soil.

2. Follow this procedure. You will get a number that is accurate within +/- 0.5

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  1. Place soil sample about ¾ full in sample jar and add distilled water to cover soil.

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  2. Cap jar and shake the soil vigorously a few times.

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  3. Let mixture stand 10 minutes to dissolve the salts in the soil.

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  4. Calibrate the pH tester with a pH 7 and a pH 10 buffer solution.

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  5. Remove the cap and place the pH tester into the wet soil slurry.

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  6. Measure pH and record measurement.

Thanks for the reply. This is a great option I will consider, but for now, I just want to do the old fashion run off test. How do I properly do it?

Testing your runoff doesn't tell you what your soil pH is. So, just do the second one.

1. Place soil sample about ¾ full in sample jar and add distilled water to cover soil
2. Cap jar and shake the soil vigorously a few times.
3. Let mixture stand 10 minutes to dissolve the salts in the soil.
4. Calibrate the pH tester with a pH 7 and a pH 10 buffer solution.
5. Remove the cap and place the pH tester into the wet soil slurry.
6. Measure pH and record measurement.

Your in soil, ph doesn't matter

I keep hearing this, but ive already been ph-ing my soil for a month now and I have problems in the PH. its obvious. So what can I do to fix it? Im using Dutch Nutrients A&B. They are getting about 500-600 PPM's of nutrients with Cal-Mag because I use RO. The leaves are showing calcium and magnesium deficiencies which I can only assume the soil is either too acidic or alkaline, causing lock out. They are looking lime greeny.

You read and heard wrong about ph in soil, the members here have given you invaluable advice.


Soil runoff will tell you nothing about the soils ph, soil has 'LIME' in it so just trust that its pre buffered anything you do will not change these facts.

Tbh if your throwing in lots of ph up 'Potassium' then expect a calmag problem.

Kingrow1 said:

You read and heard wrong about ph in soil, the members here have given you invaluable advice.


Soil runoff will tell you nothing about the soils ph, soil has 'LIME' in it so just trust that its pre buffered anything you do will not change these facts.

Tbh if your throwing in lots of ph up 'Potassium' then expect a calmag problem.

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Hmmm, this could very well be it. Maybe I should stop ph-ing the water after I add nutrients. Maybe the PH up is causing the problem. I was only adding the PH up to get the water to around 6.3-6.5 because after I add my nutrients the PH in the water goes down to about 4. so having the PH of the water at 4 isn't a problem? Also, if this helps, im using Pro-Mix BX. So do you think the PH-UP is building up over time in the soil and causing this?

Promix has lime in which neutralizes acid, maintains ph. An acidic fertilizer will just use the limes charge up a bit earlier but with 4 month grow and regular repots there should be enough lime to last easily.

My canna start dropped the ph to 3, never bothered my promix. Make the distinction between soil and hydro, billions of homegrowers go to the shop and buy bag of soil and acidic chem fert and have zero ph problems, if you have many vegetable gardens nearby youll see no one ph's anything with zero problems because they add lime or buy soil with lime in it.

Btw thats a shitload of ppm's in potassium to get from ph4 to 6.5, whats it adding, like 200ppm of ph up potassium to each feed? (which if anything mj related for veg already has a large amount of potassium!).

Kingrow1 said:

Promix has lime in which neutralizes acid, maintains ph. An acidic fertilizer will just use the limes charge up a bit earlier but with 4 month grow and regular repots there should be enough lime to last easily.

My canna start dropped the ph to 3, never bothered my promix. Make the distinction between soil and hydro, billions of homegrowers go to the shop and buy bag of soil and acidic chem fert and have zero ph problems, if you have many vegetable gardens nearby youll see no one ph's anything with zero problems because they add lime or buy soil with lime in it.

Btw thats a shitload of ppm's in potassium to get from ph4 to 6.5, whats it adding, like 200ppm of ph up potassium to each feed? (which if anything mj related for veg already has a large amount of potassium!).

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Dude, i think you may of solved my problem. Thank you Ive been thinking this, but so many people have been telling me different things. This is my first grow, so its a learning curve.

STR8QU4D5 said:

Dude, i think you may of solved my problem. Thank you Ive been thinking this, but so many people have been telling me different things. This is my first grow, so its a learning curve.

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Not in this general forum, my advice is the same as those posters above. A lot of mj growers confuse the issue of lime. If you dont like your ferts dropping the ph to 4 then find some ferts that hold the ph better rather than ph'ing them.

Personally i hate the fact that most mj ferts put so much potassium in their veg formulas, maybe in hydro or flowering but adding any more to most seems like a recipie for disaster here but such info seems scattered on such topics.

This isnt a quick fix its just a general discussion on your options and the exact system your running, which is soil in a pot (promix same thing to me). Trust more in the lime and all new growers have a mountain to climb, with more grows come better results.

Kingrow1 said:

Not in this general forum, my advice is the same as those posters above. A lot of mj growers confuse the issue of lime. If you dont like your ferts dropping the ph to 4 then find some ferts that hold the ph better rather than ph'ing them.

Personally i hate the fact that most mj ferts put so much potassium in their veg formulas, maybe in hydro or flowering but adding any more to most seems like a recipie for disaster here but such info seems scattered on such topics.

This isnt a quick fix its just a general discussion on your options and the exact system your running, which is soil in a pot (promix same thing to me). Trust more in the lime and all new growers have a mountain to climb, with more grows come better results.

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Yeah i hear ya, luckily things are only starting to show, but this has to be it. it makes sense.

MisterBlah said:

You will get a number that is accurate within +/- 0.5

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Seems like this would be i little more of a +/- differential then most would want. IMO if you truly want to test your soils ph, why not spend the few bucks need to buy a soil test kit? Seems to be rather inexpensive and usually more accurate then a +/- 0.5 as this leaves a full 1.0 threshold of possibilities. Again, just my two cents worth.

tntgreen13 said:

Seems like this would be i little more of a +/- differential then most would want. IMO if you truly want to test your soils ph, why not spend the few bucks need to buy a soil test kit? Seems to be rather inexpensive and usually more accurate then a +/- 0.5 as this leaves a full 1.0 threshold of possibilities. Again, just my two cents worth.

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Soil is a solid object, by the laws of chemistry it cannot have a ph.

Kingrow1 said:

Soil is a solid object, by the laws of chemistry it cannot have a ph.

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By no means am I a chemist, but then why in many collegiate level science labs do you spend time testing soil ph, and other nutrients within the soil? Not saying you are wrong by any means nor trying to come off as rude, however if you could provide a scholarly source on this information I would greatly appreciate the read. Just trying to continue my learning.

"What pH really measures is the concentration of hydrogen ions and hydroxyl ions in the soil. (Ions are formed when substances in the soil cause water molecules and certain other chemical compounds to break apart.) If the number of hydrogen and hydroxyl ions is the same, the soil is neutral. Since the pH scale runs from zero to 14, neutral soil has a pH of 7, the midpoint on the scale. If more hydrogen ions are present, the soil is said to be acid. Numbers decreasing from pH 7 to pH 0 indicate increasingly acid solutions. If more hydroxyl ions are present, the soil is alkaline (or basic), indicated by numbers increasing from 7 to 14. Because the pH scale is logarithmic, each number on it represents a factor of 10; that is, pH 9 is 10 times more alkaline than pH 8."


Authors: Buchanan, R.

Source: Horticulture. Jun92, Vol. 70 Issue 6, p19. 3p. 1 Illustration.

Old article, however still be used as a source at the collegiate level, which leads me to believe soil does have a pH?

tntgreen13 said:

By no means am I a chemist, but then why in many collegiate level science labs do you spend time testing soil ph, and other nutrients within the soil? Not saying you are wrong by any means nor trying to come off as rude, however if you could provide a scholarly source on this information I would greatly appreciate the read. Just trying to continue my learning.

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Messing around dude, solid objects can give no ph reading therefore they have no ph, thats basic chem but by the application of water a ph can be obtained.

Soil dosent have a ph but the water in the soil can be influenced by what it already holds and the salts held by the soil as its caution exchange capacity.

Lime added to a soil will break down and get held by the soil as part of its caution exchange capacity and thus influence the waters ph.

A soil with a low cation exchange capacity will need less lime than a soil with a higher cation exchange capacity ie promix needs less lime than a proper organic soil as promix has a cation exchange capacity of 80 and soil 130.

Hydro has no cation exchange capacity, its soil so to say is water and hence the water must be at the right ph. In soil lime keeps things at the right ph.

Im too stoned to search google for a cited paper but im sure if you look ye shall find. This and other reasons like the organic elements in soil are why its pretty fruit less to ph anything.

tntgreen13 said:

"What pH really measures is the concentration of hydrogen ions and hydroxyl ions in the soil. (Ions are formed when substances in the soil cause water molecules and certain other chemical compounds to break apart.) If the number of hydrogen and hydroxyl ions is the same, the soil is neutral. Swince the pH scale runs from zero to 14, neutral soil has a pH of 7, the midpoint on the scale. If more hydrogen ions are present, the soil is said to be acid. Numbers decreasing from pH 7 to pH 0 indicate increasingly acid solutions. If more hydroxyl ions are present, the soil is alkaline (or basic), indicated by numbers increasing from 7 to 14. Because the pH scale is logarithmic, each number on it represents a factor of 10; that is, pH 9 is 10 times more alkaline than pH 8."


Authors: Buchanan, R.

Source: Horticulture. Jun92, Vol. 70 Issue 6, p19. 3p. 1 Illustration.

Old article, however still be used as a source at the collegiate level, which leads me to believe soil does have a pH?

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It is the presence of hydronium ion relative to hydroxide
that determines a solution's pH

tntgreen13 said:

Seems like this would be i little more of a +/- differential then most would want. IMO if you truly want to test your soils ph, why not spend the few bucks need to buy a soil test kit? Seems to be rather inexpensive and usually more accurate then a +/- 0.5 as this leaves a full 1.0 threshold of possibilities. Again, just my two cents worth.

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You are right, it would be better off. But I gave him two options.

Thank you all for the advice and info. Much appreciated.