PH A Basic explanation

Aqua Man

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OK I'm going to do my best to explain PH since its something that is for the most part greatly misunderstood and can be confusing to new growers and even experienced growers alike. This will explain why we need both ppm and PH meters to give us informed information about PH

This will be a simple guide leaving out a lot of information. So lets get started with a couple of definitions to help you understand.

What is PH?

PH is a measurement of how alkaline or acid a solution is based on measuring hydrogen ions. It tells us nothing more than the ratio of acidic to alkaline elements. It does not tell us how much of each the solution contains or the alkalinity of the water.

What is alkalinity?

Alkalinity is the measurement of the waters buffering capacity (ability to neutralize acids). Its the total amount of carbonate and bicarbonate in the water that affects its ability to resist change to PH. If you know the alkalinity you can actually calculate the amount of acid of varying types needed to reach your target PH but we wont get into that.


So now we have a basic understanding of the difference lets get into some examples of source water and how alkalinity will affect PH.

RO and Distilled water

Ro and Distilled water is very low in mineral content containing carbonate or bicarbonate sources, we know this because if we test the ppm its usually under 40 and as low as 0ppm. This means it has a very low alkalinity (ability to neutralize acids) and is easily influenced by anything added that's acidic. But likewise it does not contain acid and is easily influenced by anything added that's basic. This results in a very unstable PH that can be easily influenced by anything added or anything its added to. In hydro the ideal ppm of carbonate/bicarbonate sources to provide an adequate buffer will be 50-100ppm with 75ppm being the target. Less than this and PH may swing to fast and be unstable, more and it will not drift enough and will require too much acid that could affect nutrient ratio's negatively depending on the acid used. By adding alkalinity and then acid we provide a more stable PH because adding more of either will have less impact on the overall ratio of acidic to basic elements

When used in hydro it should have alkalinity (a buffer) added back to prevent wild PH swings. Any source of carbonates, bicarbonates, silicates or hydroxides will work to create alkalinity. Sources i would recommend would be calcium carbonate, potassium bicarbonate (commonly sold as PH up) and finally what i would consider the best option is potassium silicate as it is a source of potassium and silica which are both excellent for cannabis. When using RO or distilled you will want to add back some calcium and magnesium if your nutrients are not designed for RO/distilled water as that's usually what Ro filters are removing for the majority. But most cal/mag is in the form of nitrate and provides no alkalinity (buffering capacity) so adding one of the previously mentioned or other is still a must.

When used in soil this unstable PH is actually IMO beneficial if you have a pre buffered soil (which you should) This means the water will have no impact on the PH potential (more on this later) of the soil and will almost instantly be influenced by the soil to the take on the PH of the soil makeup. This is why i feel we do not need to be PHing our nutrient solution for soil grows (unlike soiless and hydro). The soil is what will adjust the PH of our nutrient solution.

Tap Water

OK we all know tap water varies a lot form place to place and I will explain the basics of how to determine if your tap water is suitable or not for use. First we want the PPM and second we want the makeup of that ppm if available. Generally speaking the majority of the PPM makeup will be calcium carbonate. This is used to buffer the water supply and prevent acidic conditions that erode the coatings and will break down piping and leach them into the water supply such a lead (Flint Michigan ring a bell?) So we can generally assume the majority of the PPM in tap water is likely calcium carbonate but also some others like magnesium, sulfur, phospahte, iron etc. So if you have a ppm of 100-200ppm you can assume roughly 50-75% of that is calcium carbonate. Remember our target is 75ppm carbonate/bicarbonate sources to provide an ideal alkalinity (hope we are starting to see how import alkalinity is and we can't just go by PH) Now there are some cases when some sodium may be used such as sodium bicarbonate aka baking soda (can also be used as a buffer in a pinch but not recommended as a long term option) so we can google our local water report and see the makeup of the ppm in the water.

Soil PH potential

Now when we buy a prebufferd soil like most of the ones we use they come "Prebuffered" (alkalinity adjusted) what does this mean? This means the company has added amendments that when water is added the resulting PH of the water in the soil will be in a favorable range for growing our plants. Often times peat is used to lower PH and lime is used to raise PH in these soils. Just like in water we want to control the alkalinity (buffering capacity) of the soil to have a stable PH that is not easily influenced by adding things such as nutrients or other. Unlike hydro and soiless where we control the alkalinity (buffering capacity) of the water by adding it directly to the water it is applied to the soil. Which brings me back to my point of we don't need to PH our nutrient solution in soil because the soil provides the buffering and will adjust the PH. Now things like lime and peat break down slowly over time and only soluble elements will impact PH so this is how they control the PH in soil over long periods of time, because it breaks down slowly and only a small amount is soluble at a time its unlikely after a grow it has been depleted. But if we are reusing the soil we should be looking at re amending the buffering capacity before using again to ensure there is enough to last through the next grow. Often times farmers will do this once a year before seeding crops.

Effects of nutrients and source water on PH

First the PH down acids we use tend to break down much faster than the alkaline sources we use in both hydro and soil. For this reason we see a hydro systems PH generally rise over time unless something is creating more acid like decaying roots in which case we may actually see PH going down. Typically a PH increase of 0.2 in a 24 hr period is desirable and by adjusting the alkalinity we can control the PH drift. In the case of soil the acids used to bring PH down before feeding break down quickly and the alkaline and acidic buffer we have created minimizes the impact so they are really of not much benefit and have virtually no impact on long term PH potential of the soil. This is why we can't use them to lower high soil PH once we have an alkaline source buildup. However in hydro and coco PHing the nutrient solution is important because unlike soil there is not an adequate buffer established although in coco it is possible to do so.

Generally speaking the ratio's of nutrients we use will be acidic so when we get a buildup of nutrients we will almost always see PH drop. This is where you often hear ppl say flush the media. What this does is dilutes the dissolved elements and will remove some from the media in runoff.

Conversely a water source with high alkalinity can build up in the media and cause the PH potential of the soil to rise over time and in turn the PH of the water added to it. This is the reason we should look at the alkalinity of the water source not the PH as PH cannot measure the potential influence but rather only result.

Often in both circumstances its a good idea to flush the media to remove excess amount of available elements that may be affecting the PH negatively.

I'm gonna stop there and if anyone has questions i will do my best to answer them. If you have something you would like to add please do.


Aqua Man
 
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Aqua Man

Staff member
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Here is some more info from Pro Mix.


I'm not sure what the myth is?

There is no medium ph. There is potential ph. Only soluble elements can influence ph. Insoluble materials have no ph.

I can spot one thing wrong that they say. One being everytime you water you add CaC03 which is calcium carbonate. This is not true with RO and Distilled water which I covered. In the case of RO and Distilled some of the limestone added to the buffered soil will be dissolved and create a buffer. But I do agree if watering with a higher alkalinity water source it can cause a ph increase over time in alkaline sources in the media and raise ph as I covered.

Unless they are saying like I am there is no real soil pH only pH potential? If they are saying alkalinity is only influenced by water source I would say they are absolutely wrong.

Idk maybe I'm reading it wrong? But I agree with almost everything they say.

Yeah after rereading it they seem to be saying the same thing I am.
 
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I'm not sure what the myth is?

There is no medium ph. There is potential ph. Only soluble elements can influence ph. Insoluble materials have no ph.

I can spot one thing wrong that they say. One being everytime you water you add CaC03 which is calcium carbonate. This is not true with RO and Distilled water which I covered. In the case of RO and Distilled some of the limestone added to the buffered soil will be dissolved and create a buffer. But I do agree if watering with a higher alkalinity water source it can cause a ph increase over time in alkaline sources in the media and raise ph as I covered.

Unless they are saying like I am there is no real soil pH only pH potential? If they are saying alkalinity is only influenced by water source I would say they are absolutely wrong.

Idk maybe I'm reading it wrong? But I agree with almost everything they say.

The myth is that water ph influences media ph.

And ro water is covered near the end of the article.

I thought it was a good add to the thread.
 
This is so good. I knew something had to be up when i would add 1/4 tsp of my phos acid solution and it would drop my filtered water by 3 points but when added to my tap water it would only drop it by .5-1 points. Thinking since the low ppm i would add less than 1/4 tsp to my filtered water i opted for 8th tsp and still dropped it 3 points.
 
@MIMedGrower I like how they cover the ideal Alkalinity for soil... I knew it was a bit higher than hydro because we want a drift but it's nice to see actual values covered. I did not know what they would be so I learned a bit from that article. 👍

That's a very well done article

The premier horticulture (pro mix) website training center has taught me more than most sources of competent gardening info. No weed info yet as far as i know but they have many large agricultural clients so the info is spot on.

But its a bit difficult to navigate and there are tons of articles and videos.


 

Aqua Man

Staff member
Supporter
The premier horticulture (pro mix) website training center has taught me more than most sources of competent gardening info. No weed info yet as far as i know but they have many large agricultural clients so the info is spot on.

But its a bit difficult to navigate and there are tons of articles and videos.


If you will excuse me I have some reading to do... Appreciate the link bro.
 
Why not get into calculations? That's the one thing Cannabis growers need,calculators for changing pH with different substances, in mediums and solutions. Swimming pools brewers and agri have calculators, cubic foot/milk jug gardening has no calculators. If you buy bottle of pH down, it's going to say 'trial and error' under the directions on the label, they don't even give a ballpark or an example. I waste sooo much pH test drops checking and rechecking different concoctions.. I imagine a lot of people don't grow simply because they don't have time to fuck around with guessing at everything. Lots of grow lights on Craigslist.

I think bicarbonate is a big issue for a lot of growers,and it rarely gets addressed properly. Think about it. I put out tap water for the cats, when the bowl dries up, theres heavy scale buildup in the bowl. When I refill the bowl, the scale doesn't dissolve back into the water, it's permanently locked out of solution. Now replace 'cat bowl' with 'weed pot' and we see why Calmag is a hot item at the grow store.
 

Aqua Man

Staff member
Supporter
Why not get into calculations? That's the one thing Cannabis growers need,calculators for changing pH with different substances, in mediums and solutions. Swimming pools brewers and agri have calculators, cubic foot/milk jug gardening has no calculators. If you buy bottle of pH down, it's going to say 'trial and error' under the directions on the label, they don't even give a ballpark or an example. I waste sooo much pH test drops checking and rechecking different concoctions.. I imagine a lot of people don't grow simply because they don't have time to fuck around with guessing at everything. Lots of grow lights on Craigslist.

I think bicarbonate is a big issue for a lot of growers,and it rarely gets addressed properly. Think about it. I put out tap water for the cats, when the bowl dries up, theres heavy scale buildup in the bowl. When I refill the bowl, the scale doesn't dissolve back into the water, it's permanently locked out of solution. Now replace 'cat bowl' with 'weed pot' and we see why Calmag is a hot item at the grow store.
I agree bro the only issue is most do not have the availability to test for the amount of carbonate or bicarbonate in order to do so.
 
I am only offering the no stress formula I follow. I do not overthink any of my grows. I used too. I used to have a few failures too.

I use indoor and outdoor soil mixed with 50% perlite. 5 gallon buckets. I ph balance three 1 gallon jugs. The three jugs are ph5,ph6, and ph7. I rotate these a gallon at a time for the plants.

I have used all kinds of soil and there is no noticeable difference in the end product. I only add a cheap bloom booster through the 4th and 6th weeks. And I use about 25% of what the package says.

If you are like me and want to get high for the lowest price this is the way to do it. If you are after very specific traits then by all means dive into the science. I believe in it. I just believe it is a waste of time learning it all, just to grow a weed.
 
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