Do we need to pH adjust our nutrient solutions?

[InTheShed]

Greetings all! I recently had a running email conversation with the "Grower Services & Product Development Director" at ProMix (aka Premier Tech). I began the conversation by posting a question on their website, asking if I should be treating ProMix HP as soil or soil-less when mixing nutrients.

[Please note that we were not discussing hydro growing. This conversation does not apply to hydro.]

As we have all been taught, the pH range for nutrients is different for soil and soil-less media and I had been using the soil range in my ProMix and wanted to double check. His response left me confused, as he answered the question by giving me the ideal pH range for mineral soil and soil-less growing media. He did not address my question of the correct pH of the nutrient mix.

We went back and forth for a few days and his answers always referred to the pH of the media and not what we were pouring into the media. I kept trying to narrow my question and he continued in the same vein. I contained my exasperation so as not to short circuit the chain.

At one point he said this:
"It is the potential acidity or basicity of the fertilizer chemistry and the alkalinity content of your water that affects the pH of the growing medium. For the fertilizers, it is called ‘potential’ since it is determined by the chemistry and the quantity of fertilizer nutrients that are applied and the ‘potential’ they have to interact with the plant root system and influence the pH of the growing medium up or down."

All related to the medium. And the interesting use of the word "potential," but again ended it by talking about moving the pH of the growing medium.

Rather than bore you with the all back and forth, I will post this summary that I sent him in one of our last emails. He approved of this summary (italics mine):

1. Ideal pH range for mineral soil is 6.0-6.5. Soil-less growing media, such as PRO-MIX, have an ideal pH range of 5.5-6.0.

2. However, pH of nutrient water is irrelevant to the pH of any soil or growing media. It is the alkalinity of nutrient water and the potential acidity/basicity of the fertilizer(s) that influence the pH of the growing medium and root zone. For example, if the alkalinity of nutrient water is moderate or high, pH of growing medium will rise over time.

a. Plant roots are electrically charged and must maintain a neutral balance.​

b. For ammonium nitrogen (NH4) fertilizers, plants release of hydrogen ions to take up NH4. Hydrogen released is essentially acid and this drives pH down.​

c. For nitrate (NO3) form of nitrogen in fertilizers, plant exchange hydroxyl ions for NO3 uptake, which causes growing medium pH to rise.​

d. Alkalinity (CACO3) is essentially dissolved limestone. The higher the alkalinity of water, the greater tendency to raise pH of growing medium over time.​

3. It is more important to keep track of the pH of the growing medium than the pH of the nutrient solution we feed the plants.

And at the bottom of that summary I added one last direct question:
"If I’m growing in ProMix HP and I mix up the nutrient solution and it reads 7.4 pH, it is not necessary for me to adjust that number down using phosphoric acid or the like. I can pour it into the pot at 7.4 and my plants will be able to uptake those nutrients?"

His response was a direct "Yes."



-----------------------------------
We had discussions on the correct way to check the pH of soil or soil-less medium (none involved checking our nute runoff). I'll post the various methods he sent me in a different thread and post a link here. I don't want to distract from the info above!

 

[MrSauga]

Hmmm, I wont argue, but who's gonna be the guinea pig? 7.4 seems high to me.

 

[Emilya Green]

Greetings all! I recently had a running email conversation with the "Grower Services & Product Development Director" at ProMix (aka Premier Tech). I began the conversation by posting a question on their website, asking if I should be treating ProMix HP as soil or soil-less when mixing nutrients.

[Please note that we were not discussing hydro growing. This conversation does not apply to hydro.]

As we have all been taught, the pH range for nutrients is different for soil and soil-less media and I had been using the soil range in my ProMix and wanted to double check. His response left me confused, as he answered the question by giving me the ideal pH range for mineral soil and soil-less growing media. He did not address my question of the correct pH of the nutrient mix.

We went back and forth for a few days and his answers always referred to the pH of the media and not what we were pouring into the media. I kept trying to narrow my question and he continued in the same vein. I contained my exasperation so as not to short circuit the chain.

At one point he said this:
"It is the potential acidity or basicity of the fertilizer chemistry and the alkalinity content of your water that affects the pH of the growing medium. For the fertilizers, it is called ‘potential’ since it is determined by the chemistry and the quantity of fertilizer nutrients that are applied and the ‘potential’ they have to interact with the plant root system and influence the pH of the growing medium up or down."

All related to the medium. And the interesting use of the word "potential," but again ended it by talking about moving the pH of the growing medium.

Rather than bore you with the all back and forth, I will post this summary that I sent him in one of our last emails. He approved of this summary (italics mine):

1. Ideal pH range for mineral soil is 6.0-6.5. Soil-less growing media, such as PRO-MIX, have an ideal pH range of 5.5-6.0.

2. However, pH of nutrient water is irrelevant to the pH of any soil or growing media. It is the alkalinity of nutrient water and the potential acidity/basicity of the fertilizer(s) that influence the pH of the growing medium and root zone. For example, if the alkalinity of nutrient water is moderate or high, pH of growing medium will rise over time.

a. Plant roots are electrically charged and must maintain a neutral balance.​

b. For ammonium nitrogen (NH4) fertilizers, plants release of hydrogen ions to take up NH4. Hydrogen released is essentially acid and this drives pH down.​

c. For nitrate (NO3) form of nitrogen in fertilizers, plant exchange hydroxyl ions for NO3 uptake, which causes growing medium pH to rise.​

d. Alkalinity (CACO3) is essentially dissolved limestone. The higher the alkalinity of water, the greater tendency to raise pH of growing medium over time.​

3. It is more important to keep track of the pH of the growing medium than the pH of the nutrient solution we feed the plants.

And at the bottom of that summary I added one last direct question:
"If I’m growing in ProMix HP and I mix up the nutrient solution and it reads 7.4 pH, it is not necessary for me to adjust that number down using phosphoric acid or the like. I can pour it into the pot at 7.4 and my plants will be able to uptake those nutrients?"

His response was a direct "Yes."



-----------------------------------
We had discussions on the correct way to check the pH of soil or soil-less medium (none involved checking our nute runoff ). I'll post the various methods he sent me in a different thread and post a link here. I don't want to distract from the info above!

wow

 

[MrSauga]

I think it's going to be hard for most growers to control their medium pH. Many struggle with just the nute pH.

 

[InTheShed]

According to this we don't need to struggle to control our nute pH, just struggle to control our medium pH!

7.4 seems high to me.

Or it isn't after all.

wow

I know right? I kept asking different ways until he finally gave me a straight answer. I told him that was going to throw a lot of folks for a loop!

 

[Tony Urban]

But wouldnt controlling the ph of our water and nutrients help control the ph of the soil? I thought it was known science that certain nutrients have preferred ph ranges for easy transport?

 

[Mr. Magoo]

Steps out from between bottles of Doc Bud’s High Brix drenches and glances at the dust on his ph pen as he says.......”Ohhh. I forgot all about ph!”


Lol. I do love that benefit of docs kit. But I’m very interested in reading about the different ways to check ph of the medium. Can’t wait for the info, Shed!

 

[Tony Urban]

Steps out from between bottles of Doc Bud’s High Brix drenches and glances at the dust on his ph pen as he says.......”Ohhh. I forgot all about ph!”


Lol. I do love that benefit of docs kit. But I’m very interested in reading about the different ways to check ph of the medium. Can’t wait for the info, Shed!

I pulled mine out a week or two ago for the first time in 4 crops. Got a Skunk1 thats not happy and I am just trying to remove all the variables.

But before that I figured my los soils didnt require me to ph my water.

 

[Mr. Magoo]

I checked the ph of everything I poured in when I used foxfarms nutrients. I don’t miss that. Lol. I did have good results with it though.

 

[nobodyhere]

Make sense to me....
His last answer should be "Yes, depending on the dkh of the water you have been using over time".

Adjusting the ph of the water will slightly adjust dkh. Moreso if your raising it.

Effects of dkh of water are covered pretty well in the saltwater aquarium hobby.

I try to think of it (dkh or carbonate hardness) as the 'ability of the solution to stay at that ph'. It's like ph is a derivative of carbonate hardness.

I don't test for dkh of my nute solution. I know the dkh of my cistern water, maybe I should test it after applying nutes to see it's change, but considering most of the nutes I use lower ph, the effect on the solutions dkh is negligible. I would imagine it to be pretty low, considering how easy it is to adjust the nute solution.

When one goes to carefully 'adjust' the ph of solutions containing higher carbonate hardness it is a little more tricky than just adding some drops to the water.

For most of us, this will be a static factor that we really don't think about as it's not really varying in our daily nute prep. Should growers target dkh? Hell no. Should growers know if they have a hardness issue with their water? YES. Hardness is alkalinity.

Your showing your age when the question was not answered. I only say that because I am there too.

The issues in soil with dkh would be a buildup where nutes could not stay in solution in the soil. Farmers know this (we have crop rotation for this issue and others). So, the evil type 2 error occurs when someone is unknowingly giving hard water nutes over time and they get lockout even though their ph'ed water is right all the time. It happens, your on a well, and/or you have excessive co2 in water.

Hard water where grower A lives is not going to be the same as hard water where grower B lives.

Cool conversation.

 

[Homer Simpson]

However, pH of nutrient water is irrelevant to the pH of any soil or growing media. It is the alkalinity of nutrient water and the potential acidity/basicity of the fertilizer(s) that influence the pH of the growing medium and root zone. For example, if the alkalinity of nutrient water is moderate or high, pH of growing medium will rise over time.

I have always assumed that the water delivers the nutrients to the plant so the water pH is what is critical to plant health but from what I am reading here I assume that the pH of the soil or growing media is what is critical for the absorption of nutrients by the plant. And two things affect that pH, potential acidity/basicity of the fertilizer and alkalinity of the nutrient water.

“Alkalinity (from Arabic "al-qalī"[1]) is the capacity of water to resist changes in pH that would make the water more acidic.[2] (It should not be confused with basicity which is an absolute measurement on the pH scale.) Alkalinity is the strength of a buffer solution composed of weak acids and their conjugate bases. It is measured by titrating the solution with a monoprotic acid such as HCl until its pH changes abruptly, or it reaches a known endpoint where that happens. Alkalinity is expressed in units of meq/L (milliequivalents per liter), which corresponds to the amount of monoprotic acid added as a titrant in millimoles per liter.”

So how do we determine the alkalinity of our water since that is the variable not pH like everyone assumes?

 

[Mr. Magoo]

I’m not sure how hard my water actually is, but I know it’s hard. Any cloth that gets wet ends up pretty stiff when it dries....like washcloths. I filter my water before adding anything to it for my girls. I’m not sure how this effects the hardness of the water. Plants seem to be ok with it but I would love to learn more about it!

 

[nobodyhere]

I have always assumed that the water delivers the nutrients to the plant so the water pH is what is critical to plant health but from what I am reading here I assume that the pH of the soil or growing media is what is critical for the absorption of nutrients by the plant. And two things affect that pH, potential acidity/basicity of the fertilizer and alkalinity of the nutrient water.

“Alkalinity (from Arabic "al-qalī"[1]) is the capacity of water to resist changes in pH that would make the water more acidic.[2] (It should not be confused with basicity which is an absolute measurement on the pH scale.) Alkalinity is the strength of a buffer solution composed of weak acids and their conjugate bases. It is measured by titrating the solution with a monoprotic acid such as HCl until its pH changes abruptly, or it reaches a known endpoint where that happens. Alkalinity is expressed in units of meq/L (milliequivalents per liter), which corresponds to the amount of monoprotic acid added as a titrant in millimoles per liter.”

So how do we determine the alkalinity of our water since that is the variable not pH like everyone assumes?

You follow the instructions above, there are test kits. And there are about 4 different ways I know of to express it that are not zero conversions. I don't know of anyone other than chemists who use meq/l or test with kits that do.

I have the test kits, but am I going to test my nute water...god no. This is a constant, and if you try to change it I promise your going to open a big ass can o worms that involves more issues and testing.

If you don't like the hardness of your water, get a filter, ro, mixed bed di, or rodi, or change your source. End of story. Or find out how difficult it is to add out of solution hardness to water and get it to ph anywhere near where you want it (forget adding nutes).

So....for those at home, don't target alkalinity, but change your source.

 

[Homer Simpson]

You follow the instructions above, there are test kits. And there are about 4 different ways I know of to express it that are not zero conversions. I don't know of anyone other than chemists who use meq/l or test with kits that do.

I have the test kits, but am I going to test my nute water...god no. This is a constant, and if you try to change it I promise your going to open a big ass can o worms that involves more issues and testing.

If you don't like the hardness of your water, get a filter, ro, mixed bed di, or rodi, or change your source. End of story. Or find out how difficult it is to add out of solution hardness to water and get it to ph anywhere near where you want it (forget adding nutes).

So....for those at home, don't target alkalinity, but change your source.

Okay so if I have this right I don’t worry about pH because it doesn’t really affect the pH of the soil instead the alkalinity does but changing alkalinity of water is a nightmare so get a source which I assume would have zero alkalinity such as ro water? But that means since you are using a water with an alkalinity you can’t alter you have to hope your, potential acidity/basicity of the fertilizer(s), the other variable, doesn’t change?

 

[FelipeBlu]

For Pro-Mix, which has a high CEC, a high alkalinity nutrient solution (are you adding lots of CalMag?), will change the media, as the plant takes what it needs and leaves the rest to over-accumulate.

Now with something like hempy with straight perlite, which has zero CEC, your medium is the same as your nutrient solution. And you replace it with fresh every 2-3 days or so.

 

[dr.h00k]

...I believe that everyone tends to overthink the science or chemistry of salt based nutrient feeding, spending way too much money on "designer" nutes and fancy meters for measuring(my mind says...promix leans towards a soil medium)...I've been using ProMix HP and EWC's and organic amendments for the past couple runs, with better results than previous bottled/granular "hyped" brands used in the same blend (less the amendments)and premium potting soil(Granted, my lighting has been upgraded)...I've only used litmus paper and some powdered test kits and run slurry tests...if I'm anywhere between 6 and 7...I feel good to go...Missus h00k did buy me a meter once...one of those triple light/moisture/PH meters...on clearance at 5.99!??...thanks Honey!......
...with Monsanto buying up major nute company's and all that fall under their umbrella, it might be prudent to think more about growing more naturally, and knowing what's going into one's girlz...I follow a few gardens that are run organically, but one has to only look at Stank's efforts in a DIY soil build that is consistently producing contest winning produce...anyway's...thanks shed!......cheerz...h00k......

 

[nobodyhere]

Okay so if I have this right I don’t worry about pH because it doesn’t really affect the pH of the soil instead the alkalinity does but changing alkalinity of water is a nightmare so get a source which I assume would have zero alkalinity such as ro water? But that means since you are using a water with an alkalinity you can’t alter you have to hope your, potential acidity/basicity of the fertilizer(s), the other variable, doesn’t change?

you would not want zero alkalinity water.

I would not change anything until you understand what your trying to change. Read up on how it applies to pools, farming, aquariums, ponds, etc. Then after you understand it, decided for yourself that you don't want to adjust it.

ph of nutes over the short term does not matter. Over the length of the grow, it does matter. Soil has alkalinity. It can be changed through error or normal practice with time.

I would not go throwing ph3 stuff on a plant, but I throw 'off' ph low ppm on my plants when in a hurry, the soil, or soilless mix will adjust for this.

But on a 100 day veg plant with a 70 day flower and you give off ph'ed high ppm nutes for 4 months, you will have issues with the plants development.

By getting the pH of the nute solution within a workable range, the soil or media will do the rest. dkh should not be a factor as your not 'stressing' it.

I am not a chemist, but took chem. I understand it, and am probably not the best to explain it.

 

[Homer Simpson]

you would not want zero alkalinity water.

I would not change anything until you understand what your trying to change. Read up on how it applies to pools, farming, aquariums, ponds, etc. Then after you understand it, decided for yourself that you don't want to adjust it.

ph of nutes over the short term does not matter. Over the length of the grow, it does matter. Soil has alkalinity. It can be changed through error or normal practice with time.

I would not go throwing ph3 stuff on a plant, but I throw 'off' ph low ppm on my plants when in a hurry, the soil, or soilless mix will adjust for this.

But on a 100 day veg plant with a 70 day flower and you give off ph'ed high ppm nutes for 4 months, you will have issues with the plants development.

By getting the pH of the nute solution within a workable range, the soil or media will do the rest. dkh should not be a factor as your not 'stressing' it.

I am not a chemist, but took chem. I understand it, and am probably not the best to explain it.

I appreciate the input and think you explained it very well and it was helpful, thanks...

 

[InTheShed]

His last answer should be "Yes, depending on the dkh of the water you have been using over time".

He did say that, in what he said above.

ph'ed high ppm nutes for 4 months

You still don't believe him, which is fine.

The alkalinity of your water and the potential (not actual) acidity/basicity of the fertilizer will determine what happens to the pH of your medium. The potential acidity/basicity of the fertilizer is determined by whether your nitrogen is ammonium or nitrate based.

Steps out from between bottles of Doc Bud’s High Brix drenches and glances at the dust on his ph pen as he says.......”Ohhh. I forgot all about ph!”

If you're watering your plant, the alkalinity of your water will change the pH of HB soil just like any other. Even organic and LOS growers have to at least know the alkalinity of their water, as the pH of the soil will rise over time with highly alkaline water. High enough to affect uptake of certain nutrients? I'm sure with very alkaline water and a long enough grow, yes. So your pH pen can collect dust until you decide to slurry test your soil. Then you can brush it off!

For Pro-Mix, which has a high CEC, a high alkalinity nutrient solution (are you adding lots of CalMag?), will change the media, as the plant takes what it needs and leaves the rest to over-accumulate.
Now with something like hempy with straight perlite, which has zero CEC, your medium is the same as your nutrient
solution. And you replace it with fresh every 2-3 days or so.

If you have build-up of anything in your medium you can stress the plant, which is why corrective flushing often works. And hempy is hydro. Your pH needs to be tested with every watering. I stated at the top this does not apply to hydro.

By getting the pH of the nute solution within a workable range, the soil or media will do the rest. dkh should not be a factor as your not 'stressing' it.

This is the opposite of what he is saying. And you're ignoring his point about the source of nitrogen in your nutes.

Your showing your age when the question was not answered.

I have no idea what that means.

But wouldnt controlling the ph of our water and nutrients help control the ph of the soil? I thought it was known science that certain nutrients have preferred ph ranges for easy transport?

The roots interact with the pH of the medium to uptake those nutrients, so the pH of the medium is what determines
which nutrients are available.

I’m not sure how this effects the hardness of the water. Plants seem to be ok with it but I would love to learn more about it!

I checked online to find the average alkalinity of my tap water from my water company. It's on the low end, which means the source of my nitrogen will have a greater effect on the pH of my medium.



I don't have the science background to defend what he says, but I will come back and correct the incorrect or incomplete readings of what he said. And it's very possible to do exactly what you were doing and have it come out fine, or stop doing what you're doing and also come out fine. The reason it's working is unrelated to pH-adjusting our nutes before they go in and completely related to the hardness of our water and the source of the nitrogen in our fertilizer. That also could be the reason something is not working.

 

[nobodyhere]

No shed, I am not ignoring N. If you look back at my journals over the past 20 months or so, you will see what type of N I give, and what type I rarely give.

I understand what he is saying very well, but am trying to give a 'closeabouts' explanation so people are not ordering alkalinity test kits off amazon and calcium carbonate or soda ash or lime to try to adjust dkh in a 3 gallon pot of soil.