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Improved runoff method for testing soil pH

oldster

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If you are a soil grower the best way to know what is going on with the pH of the soil is with a good pH probe like the Accurate 8.

It is very common for soil pH to vary over time which affects the plants ability to absorb needed nutrients. Plant problems caused incorrect soil pH are probably the most common issue for new growers so monitoring soil pH regularly will help keep your grow on the right track.

If you don't have a good soil pH probe (the cheap ones sold in garden stores are a waste of money) here is the next best method to check your soil pH.

The Pour Thru Method for Testing Container Media

1. water containers to saturation (so that a few drops of water come out of the bottom of the container) with the normal irrigation water they have been receiving

2. after container has drained for one hour, place a saucer under the container

3. pour enough distilled (DI) water on the surface of the container to get 50 mL (1.5 fluid ounces) of leachate to come out of the bottom of the container (Table 1)

4. collect leachate for pH and EC testing

5. calibrate pH and EC meters

6. measure pH and EC of samples

note: don't worry if you don't have an EC meter

>>> If your runoff pH is higher than your starting (water) pH, use this equation to determine your soil pH:*
Soil pH = Runoff pH + Difference

If your runoff pH is lower than your starting pH, us this equation:
Soil pH = Runoff pH - Difference.

For example, say your the starting pH of your solution before it goes in is 6.5 and the pH of your runoff is 7.0. The difference is +0.5, so using the above equation:
Soil pH = 7.0 + 0.5*
Soil pH = 7.5

If your starting pH is 6.5 and your runoff is 6.0, your difference is -0.5 and using the above equation:
Soil pH = 6.0 - 0.5
Soil pH = 5.5
 
Last edited:

briman

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Great tutorial oldster! Needed a sticky on this for a while! Max rep to ya!:slap: Here step into that!
 

Waira

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Cheers Oldster! :cool:...a nice find from elsewhere,... :brow:--- but good info is good info, so over it came! Many of us feel that this is a dubious method in the first place, due to several potential sources of measurement error inherent in it... but it'll do in a pinch if done with this in mind.... cross contamination of run-off sampling is a common one, so folks, use a clean, dry saucer to collect from, and ditto for the cup or whatever you test in,.... better still, let the sample sit for several minutes to let as much larger particulate matter settle to the bottom as is feasible, and test the clearer solution near the top,...make sure you're still fully submersed though!
 

briman

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Max rep to you BOTH! Didn't know you posted this else where, Waira! Great info! Great directions to boot!
 

FreeinAK

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I'm very new at this (as a matter of fact, I haven't even ordered my seeds yet). But I have spent hours upon hours comparing products online. This seems (correct me if I'm wrong) far more accurate than even the expensive meters. I'm bug-eyed from reading reviews, but accuracy seems to be real problem in the meters. http://www.amazon.com/Luster-Leaf-1662-Professional-Tests/dp/B003JCMKEK/ref=sr_1_15?ie=UTF8&qid=1427661416&sr=8-15&keywords=ph+test+kit

This one only measures 10 times per test (the other tests being nitrogen, phosphorus and potash). I figure I'd only test one plant each time I tested (since I plan to treat all plants identically), and perhaps only once or twice per grow cycle unless I'm seeing problems.

I'd get a mid-priced meter too for just daily GP (maybe this one: http://www.amazon.com/gp/product/B006TDCM9Y/ref=s9_simh_gw_p86_d0_i5?pf_rd_m=ATVPDKIKX0DER&pf_rd_s=desktop-3&pf_rd_r=02MW3NZFSJRPDJSQ31C8&pf_rd_t=36701&pf_rd_p=1970567742&pf_rd_i=desktop). But am I wrong to not want to trust a meter for something so important?
 

oldster

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If you are getting the soil probe to measure soil pH forget it. The second item under questions and answers confirms the pH mode did not work. The cheapest working soil pH meter that I am aware of is the Accurate 8 $60-$70.

As to the test kit I would skip it as well and invest in a digital pH meter. I know some folks here bash them but I have one expensive and two cheap pH meters and I like the cheap ones the best. I have never found them to be off more that .2 when I calibrate them and I get a stable reading in under 10 seconds. Here is what I purchased http://www.amazon.com/Etekcity-pH-009-Digital-Pocket-Sized-Quality/dp/B00CH3QZSE/ref=sr_1_1?ie=UTF8&qid=1427667611&sr=8-1&keywords=Etekcity+pH-009+Digital+Pocket-Sized+Pen+Type+pH+Meter

Get some pH 7.0 calibration solution (I use General Hydroponics brand) and check calibration one a month or anytime you forget to put the cap back on for more than a few minutes. I always rinse mine with distilled water after each use to keep the bulb clean

A digital pH meter is a lot more accurate then any of the test kits
 

Need4Weed

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I like the cheap ph meters too, Etekcity, Dr. Meter, ect ... Some of these cheap brands are shipped with a moisture sponge, (for lack of a better word), that is usually dried up. You need to moisture them back up before attempting to remove particles from the probe area as the probe is easily damaged. I used calibration fluid and continue to pour a little in the cap after every using, (after rinsing with distilled water). Just my 2 cents ... :toke: :peace:
 
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