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Does the PH really matter?
Posted 11 February 2008 - 04:58 PM
How do I measure pH?
The best way is a wateproof digital pen. These are typically accurate to 0.1 or better and cost anywhere from $20 to several hundred dollars. Hydroponic growers need this accuracy as the pH range is much more narrow than that of soil/less media.
Dipsticks can be had that change color for comparison against a chart. They typically have an accuracy of about 0.5. pH paper, also sold as nitrazine paper measures by color change as well and is also accurate to about 0.5. They are sold for around $10.
Kits that use a sample of water into which a couple drops of "developer" are added are the least desirable devices. They depend upon comparing the color of the water sample to a chart and are often only accurate to 1.0. If the water sample is not colorless before adding the developer, the kit's accuracy will be skewed from the beginning. These are available for about $5.
Do I measure pH before or after adding nutrients, etc to the water?
Add everything to the water and mix it well, then measure the pH. Nutrients, growth stimulants, etc will alter the pH, so it's best to adjust it right before the water is applied to the plants.
I've added all the stuff to my water and the pH is x.x, what now?
If growing in a soil/less medium the pH should be approximately 6.5 and in hydroponic media the pH should be about 6.0 before application.
To lower the pH an acid must be added to the water and to raise the pH a base must be added. There are products available on the shelf called "pH up" & "pH down". They work well. There are also household products that will accomplish the same goal.
Household "pH downs"
Vinegar (white distilled, apple cider, wine...)
Household "pH ups"
Tap water (my preference) Municipal water is often pH'd above 7.0 to improve palatability (taste).
Baking Soda (NOT baking powder)
Baking soda is sodium bicarbonate. Its use can cause problems so I advise against it. It works well in a pinch AND when used infrequently. Increased sodium concentration in the medium displaces K and may cause a condition appearing as K deficiency. There is a maxim in chemistry which states "water follows sodium"; if the sodium concentration in the medium is high, water can actually be wicked AWAY from the roots causing wilt.
How much pH up or pH down do I add to change the pH of my water by 1.0?
That all depends upon the quality of the initial water sample. Quality is determined by ppm/tds/ec measurement. Water samples with lower ppm/tds/ec measurements will require LESS acid or base to change the pH of the sample as compared to those with higher tds/ppm/ec numbers. "Hard water" will have high tds/ppm/ec.
Regardless of what a product's label states, some trial and error has to occur. The manufacturer can't know the purity of any given water sample.
Add a little of the product, mix well, and measure the pH. Once you get the pH in the proper range note the amount of product you added. Next time add that amount to your water and measure to see if the pH comes out in the same range. Once you've reproduced the pH several times you can safely put the pH meter away until the plants shows signs of distress. That said, any time the source of water changes OR the additives change (different brand, new additive, etc) the same procedure will need to be performed.
I wouldn’t recommend using a probe that you place in the soil. The pH pens are much more accurate.
Here are the methods of testing your soil pH. I’ve put both methods here, but the one I use and the one you’ll most likely want to use is the runoff method because it’s much faster and easier to do. After you get a handle on what’s happening with your pH you can dial in your soil and nutrient regiment so you won’t need to test the pH very often.
Both methods below will work. I put the “collecting soil sample” tutorial because it’s considered to be the only real scientific way of testing the soil pH. I’ve found the runoff method to be very reliable if done correctly, and again, it’s the one I use.
Collecting soil and mixing with distilled water method:
Soil Sample Preparation
1. Calibrate the pH pen.
2. Scoop up loose soil samples with a clean, dry plastic
spoon. Avoid touching the soil with your hands to prevent contaminating the sample. Take soil sample as deep as possible without affecting roots.
3. Remove any stones and crush any clumps of soil.
4. Fill up your sample soil up to 3/4 and add distilled water to the jar. Cap the jar tight and shake it vigorously a few times. Let the mixed sample stand for 5-10 minutes to dissolve the salts in the soil.
5. Dip the pH pen electrode into the wet soil slurry. Take the reading when it stabilizes.
6. Rinse your pH pen thoroughly in clean water between each use.
Soil pH Data
The pH test value in this procedure is accurate to ±0.5 pH or better (usually ±0.2 pH). The soil sample preparation and test procedure is adapted from accepted laboratory methods. Most soil pH measurement cannot achieve ±0.1 pH accuracy, even with elaborate laboratory procedures and expensive pH instruments.
Recommendations for Best Results
Prepare and run at least three tests of the same soil sample to confirm results. Minor (< ±0.2 pH) or no differences between readings indicate good technique and high confidence in results. Larger differences (> ±0.5 pH) require more testing.
Testing runoff after watering method:
1. Use distilled or reverse-osmosis water. This is inert water that will readily take on the active soil pH.
2. Do not adjust the pH of the water being used for the test, as that will buffer the results in the direction of the pH adjustment.
3. Scuff the surface of the soil to allow for uniform wetting and drainage of the soil.
4. Poor water in slowly until the soil is saturated with water. You may get a small amount of runoff, but it’s best to just saturate the soil.
5. Wait 30 minutes. Chill out and smoke one.
6. Add the amount of water that will give you a small concentrated amount of runoff.
7. Test the runoff.
I like to see that the runoff, for my soil anyway, is rust colored. That lets me know that there are a lot of constituents of the soil present in the sample as opposed to a more clear runoff that would be indicative of the water running down the side of the pot or not filtering nicely through the medium. In other words, get that water dirty.
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Posted 12 February 2008 - 09:34 AM
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Posted 13 December 2009 - 11:30 PM
Posted 13 December 2009 - 11:33 PM
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Posted 13 December 2009 - 11:56 PM
can i use pool acid to drop the ph ?
What is its main ingredients???
Posted 20 February 2010 - 12:18 AM
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Posted 20 February 2010 - 12:59 AM
'I wouldn’t recommend using a probe that you place in the soil" why not are they not as consistent and for arguemnt sake say if U where to use do thee same methods apply ?
As far as soil probes go, they're pretty much pieces of junk. The only way to really know if you're measurement was accurate, would be to test it using some other method, and at that point the soil probe becomes obsolete!
Thanks again for this post.
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Posted 18 August 2010 - 04:56 AM
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Posted 06 August 2012 - 02:14 AM
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Posted 06 August 2012 - 11:06 AM
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Posted 06 August 2012 - 03:49 PM
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Posted 07 August 2012 - 12:51 PM
Posted 03 December 2015 - 12:13 AM
This is a great topic. I love to hear people talk about ph, seems so many people
dont understand it. I love the chart posted above by Lumix, which clearly shows
which nutes get locked out at different ph ranges.
I read headpawtheads post closely and am confused by it.
Why in the world would you test your water and nutes and adjust the ph too?
and than test your runoff? This makes no sense to me.
1-test water and nutes, write down ph value for later reference <value for arguments sake is ten>
place plant on a plate or something simular and catch your run off....
test your run off....<value for arguments sake is five>
so in this instance, my soil has a runoff ph of 5 and my water and nutes are 10
This means I need to raise the ph of my water and nutes to 11.5 (not lower it)
That extra 1.5 we just added will bring our run off up to an acceptable ph of 6.5
- Bueller likes this
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