Irrigation water ph and alkalinity for promix hp soilless substrate

PH and alkalinity are not the same thing but can be mixed up easily because of the terms alkalinity and alkaline (Basicity)
PH is measuring acid vs basic H+ ions. It has no actual impact on your growing medium PH,
water Alkalinity is a measurement of bicarbonate / carbonate (CaC03 ppm) the more CaCo3 the more buffering capacity the water has and can drive your PH up.
(Promix website)


Check out this link to the promix website they have some very good resources with a nice video to help explain things... everyone likes videos
It was helpful in clarifying if and why acid injection may be necessary depending on your water alkalinity. to find out how much bicarb is in your water from the tap you can look at your city water report and find the CaC03 levels for an idea of how much buffering capacity the water you use has. This is why RO water has no buffering capacity and requires little to no acid injection to bring down PH to optimal ranges.

Remember that just because you feed at 6.5 doesn't mean the root zone is at 6.5. You may wish to grab a good soil pH meter like the blue lab and check what your root zone pH is running. Most peat based mixes I have run will tend to crash around week 4 or 5, pH ending up way lower than your target despite feeding at the proper pH. When this is the case you will need to offset the pH with corrective feeds.

kingkush4200 said:

PH and alkalinity are not the same thing but can be mixed up easily because of the terms alkalinity and alkaline (Basicity)
PH is measuring acid vs basic H+ ions. It has no actual impact on your growing medium PH,
water Alkalinity is a measurement of bicarbonate / carbonate (CaC03 ppm) the more CaCo3 the more buffering capacity the water has and can drive your PH up.

Water Alkalinity vs pH - What's the Difference? | PT Growers and Consumers

Learn about the distinction between water alkalinity vs pH, understand their significance in horticulture, and select the right fertilizer accordingly.

www.pthorticulture.com

Check out this link to the promix website they have some very good resources with a nice video to help explain things... everyone likes videos
It was helpful in clarifying if and why acid injection may be necessary depending on your water alkalinity. to find out how much bicarb is in your water from the tap you can look at your city water report and find the CaC03 levels for an idea of how much buffering capacity the water you use has. This is why RO water has no buffering capacity and requires little to no acid injection to bring down PH to optimal ranges.

Click to expand...

Thanks for the clarification. I will admit that I didn't even think the alkalinity measurement OP was doing was that. I thought they were talking about the type of alkalinity testing I was used to when I was into reef keeping and it didn't occur to me that they were talking about the buffering capacity of the water.

Renfro said:

Remember that just because you feed at 6.5 doesn't mean the root zone is at 6.5. You may wish to grab a good soil pH meter like the blue lab and check what your root zone pH is running. Most peat based mixes I have run will tend to crash around week 4 or 5, pH ending up way lower than your target despite feeding at the proper pH. When this is the case you will need to offset the pH with corrective feeds.

Click to expand...

I'm considering getting a Blue Lab pH soil pen, as you've said it does liquid as well.

How often do you perform soil pH checks, and how do you schedule them? A few plants each week random? Every plant once a week?

Renfro said:

Remember that just because you feed at 6.5 doesn't mean the root zone is at 6.5. You may wish to grab a good soil pH meter like the blue lab and check what your root zone pH is running. Most peat based mixes I have run will tend to crash around week 4 or 5, pH ending up way lower than your target despite feeding at the proper pH. When this is the case you will need to offset the pH with corrective feeds.

Click to expand...

Doesn't pre-amended garden lime help with this? I amended the last grows I did in ProMix HP with 2TBSP of garden lime for every gallon of soil. Then, when I flipped to flower, I top dressed and mixed 1TBSP/gal into the top couple of inches, and I didn't have any pH issues.

TreeFarmerCharlie said:

Doesn't pre-amended garden lime help with this? The I amended the last grows I did in ProMix HP with 2TBSP of garden lime for every gallon of soil. Then, when I flipped to flower, I top dressed and mixed 1TBSP/gal into the top couple of inches, and I didn't have any pH issues.

Click to expand...

Sure it can help, you still need to monitor things. Lime is a little bit of a guessing game, easy to overdo it and it does slowly become exhausted. I always recommend watching the pH of your medium, it can do funny things. I have seen mixes stay good for a while and then crash.

spek9 said:

I'm considering getting a Blue Lab pH soil pen, as you've said it does liquid as well.

How often do you perform soil pH checks, and how do you schedule them? A few plants each week random? Every plant once a week?

Click to expand...

u stick the tester in the soil when u have the cover on the probe so u can make the hole using the cover and not the probe. take cover off then I wash the probe between plants and putting it back in to storage put probe in hole and let it stabilize. I usually just check the soil when it looks like my plant is off.

Renfro said:

Sure it can help, you still need to monitor things. Lime is a little bit of a guessing game, easy to overdo it and it does slowly become exhausted. I always recommend watching the pH of your medium, it can do funny things. I have seen mixes stay good for a while and then crash.

Click to expand...

Yeah, the first time I tried this I did slurry tests every couple of weeks. Some guy mentioned to me that he's used that method for quite awhile, specifically with ProMix HP, and he hasn't had any pH issues since he started doing that so I gave it a shot and it worked well for me.

Yah, promix even says on the website it is only really good for 1 grow.... obviously they want you to buy more... Ultimately after 1 run the soil has likely used up much of its wetting agent and the calcitic and dolomite lime agents no longer can buffer the soil so you will potentially begin having issues. if you just add more wetting agent and lime it is supposedly fine to keep using. I tend to just buy new promix and toss my old stuff in the garden. but definitely not necessary.


The Promix website is actually a great source of knowledge, and they often provide scholarly resources so that's nice....

Renfro said:

Remember that just because you feed at 6.5 doesn't mean the root zone is at 6.5. You may wish to grab a good soil pH meter like the blue lab and check what your root zone pH is running. Most peat based mixes I have run will tend to crash around week 4 or 5, pH ending up way lower than your target despite feeding at the proper pH. When this is the case you will need to offset the pH with corrective feeds.

Click to expand...

Hi how do you correct ph of the medium. The promix representatives say you cannot change the ph of the medium with ph up or down?

kingkush4200 said:

PH and alkalinity are not the same thing but can be mixed up easily because of the terms alkalinity and alkaline (Basicity)
PH is measuring acid vs basic H+ ions. It has no actual impact on your growing medium PH,
water Alkalinity is a measurement of bicarbonate / carbonate (CaC03 ppm) the more CaCo3 the more buffering capacity the water has and can drive your PH up.
View attachment 4579120 (Promix website)

Water Alkalinity vs pH - What's the Difference? | PT Growers and Consumers

Learn about the distinction between water alkalinity vs pH, understand their significance in horticulture, and select the right fertilizer accordingly.

www.pthorticulture.com

Check out this link to the promix website they have some very good resources with a nice video to help explain things... everyone likes videos
It was helpful in clarifying if and why acid injection may be necessary depending on your water alkalinity. to find out how much bicarb is in your water from the tap you can look at your city water report and find the CaC03 levels for an idea of how much buffering capacity the water you use has. This is why RO water has no buffering capacity and requires little to no acid injection to bring down PH to optimal ranges.

Click to expand...

I’m having trouble understanding. So if my well water ph is 8.2 and 60 ppm alkalinity. Would I benefit from using ph down or use my water as is

Tommy125 said:

I’m having trouble understanding. So if my well water ph is 8.2 and 60 ppm alkalinity. Would I benefit from using ph down or use my water as is

Click to expand...

Short answer: YES you can use that water without adding PH down.

PH of the water is truly only important if you are growing hydroponically, because you do not have the medium to buffer the water to the appropriate PH for nutrient absorption.

With your water being a very low 60ppm alkalinity you are fine feeding it straight water with no acid injection "PH DOWN" , the water straight up as is will have minimal impact on your overall PH, even without adding nutrients.

If water is passed through a reverse osmosis unit, then alkalinity is very low, so the water does not cause the pH of the growing medium to rise quickly. Reverse osmosis units are not necessary for most water sources if the fertilizer is properly matched to the water profile and the crop grown.


I have water of 7.5pH 160ppm alkalinity from the tap, so based off this chart I could expect that in 49days of using my water straight i could expect my mediums PH to be roughly around 6.7 ishhh.

You with 60ppm alkalinity could expect maybe id guess 6.5 ish

In promix, you have 3 factors that influence PH.

1)Fertilizer PH. What kind of fertilizer are you using? some are more acid some are basic depending on the type of nitrogen they use

2)Water Alkalinity (CaC03): your 60ppm is very low so it has a very weak ability to buffer PH I bet simply adding your nutrients would drop your PH down into the 6.5 range without any PH down. my 7.5PH 160 ppm alkalinity will go to around 6.2-6.5 after I add my fertilizers. I don't actually know what my final alkalinity CaC03 ppm is after nutrients ends up at because I don't have a test kit.

3)Medium: buffering capacity Promix is naturally acidic but they add calcitic and dolomite lime, this takes time to activate (around 1 week of being moist) and until it has completely been activated u can find promix to have a very low PH ... 5.0 when its fresh.

Here is a simple experiment that I did when i was having some issues and was not really understanding PH and alkalinity and its influence on my soil ph,

Take fresh Promix and old used up promix with no more buffer left over.
put them into a beer cups and label them the more controls you have the more data, the more you can conclude etc. Makes for a better experiment.

add water 2:1 ratio test samples on days 1,5,10,15..... with ph/tds pens for as long as youd like. you will have to cover the cups to prevent evaporation
Fresh promix

Cup 1 - water 7.5 ph - 160ppm CaC03 = PH measurement in order = 5.1 / 5.8 / 6.1 / 6.2
Cup 2 - water with acid injection 5.5PH unknown CaC03 = PH measurement in order = 4.9 / 5.4 / 6.1 / 6.2
Cup 3 - water with fertilizers 6.4PH unknown CaC03 PH measurement in order = 5.0 / 5.4 / 6.1 / 6.2

Old promix
Cup 1 water 7.5 ph - 160ppm CaC03 = PH measurement in order = 6.6 / 6.8 / 6.7 / 6.6
Cup 2 water with acid injection 5.5PH unknown CaCo3 = PH measurement in order = 6.6 / 6.4 / 6.3 / 5.9
Cup 3 Water with fertilizers 6.4PH unknown CaC03 = PH measurement in order 6.6 / 6.4 / 6.2 / 6.1

This showed to me that fresh promix is a very low PH when it has not be activated by water, and regardless of the water ph/CaC03 fresh promix will buffer to 6.2ish in 10 days due to the lime. If you transplant into fresh promix you can experience PH fluctuations for a few days, which is one of the main reasons I actually did this test.

The old promix you can see that the buffer is mostly gone as it no longer maintains at 6.2ph at 10days. and that water Alkalinity can have a more dramatic influence on PH in used up promix with no left over lime. I was expecting to see lower ph numbers due to the peat moss. but the alkalinity in the water seems to have buffered the PH to stay in the 6s showing the impact of alkalinity at 160PPm.

kingkush4200 said:

Here is a simple experiment that I did when i was having some issues and was not really understanding PH and alkalinity and its influence on my soil ph,

Take fresh Promix and old used up promix with no more buffer left over.
put them into a beer cups and label them the more controls you have the more data, the more you can conclude etc. Makes for a better experiment.

add water 2:1 ratio test samples on days 1,5,10,15..... with ph/tds pens for as long as youd like. you will have to cover the cups to prevent evaporation
Fresh promix

Cup 1 - water 7.5 ph - 160ppm CaC03 = PH measurement in order = 5.1 / 5.8 / 6.1 / 6.2
Cup 2 - water with acid injection 5.5PH unknown CaC03 = PH measurement in order = 4.9 / 5.4 / 6.1 / 6.2
Cup 3 - water with fertilizers 6.4PH unknown CaC03 PH measurement in order = 5.0 / 5.4 / 6.1 / 6.2

Old promix
Cup 1 water 7.5 ph - 160ppm CaC03 = PH measurement in order = 6.6 / 6.8 / 6.7 / 6.6
Cup 2 water with acid injection 5.5PH unknown CaCo3 = PH measurement in order = 6.6 / 6.4 / 6.3 / 5.9
Cup 3 Water with fertilizers 6.4PH unknown CaC03 = PH measurement in order 6.6 / 6.4 / 6.2 / 6.1

This showed to me that fresh promix is a very low PH when it has not be activated by water, and regardless of the water ph/CaC03 fresh promix will buffer to 6.2ish in 10 days due to the lime. If you transplant into fresh promix you can experience PH fluctuations for a few days, which is one of the main reasons I actually did this test.

The old promix you can see that the buffer is mostly gone as it no longer maintains at 6.2ph at 10days. and that water Alkalinity can have a more dramatic influence on PH in used up promix with no left over lime. I was expecting to see lower ph numbers due to the peat moss. but the alkalinity in the water seems to have buffered the PH to stay in the 6s showing the impact of alkalinity at 160PPm.

Click to expand...

Wow great information, thank you. Did you end up using ph down for successful crops or did you use your water as is. A promix representative told me optimal medium ph is 5.6 to 6.2. Did your soil ph climb far past 6.2 and were you using a soil ph probe or testing runoff water?

kingkush4200 said:

Here is a simple experiment that I did when i was having some issues and was not really understanding PH and alkalinity and its influence on my soil ph,

Take fresh Promix and old used up promix with no more buffer left over.
put them into a beer cups and label them the more controls you have the more data, the more you can conclude etc. Makes for a better experiment.

add water 2:1 ratio test samples on days 1,5,10,15..... with ph/tds pens for as long as youd like. you will have to cover the cups to prevent evaporation
Fresh promix

Cup 1 - water 7.5 ph - 160ppm CaC03 = PH measurement in order = 5.1 / 5.8 / 6.1 / 6.2
Cup 2 - water with acid injection 5.5PH unknown CaC03 = PH measurement in order = 4.9 / 5.4 / 6.1 / 6.2
Cup 3 - water with fertilizers 6.4PH unknown CaC03 PH measurement in order = 5.0 / 5.4 / 6.1 / 6.2

Old promix
Cup 1 water 7.5 ph - 160ppm CaC03 = PH measurement in order = 6.6 / 6.8 / 6.7 / 6.6
Cup 2 water with acid injection 5.5PH unknown CaCo3 = PH measurement in order = 6.6 / 6.4 / 6.3 / 5.9
Cup 3 Water with fertilizers 6.4PH unknown CaC03 = PH measurement in order 6.6 / 6.4 / 6.2 / 6.1

This showed to me that fresh promix is a very low PH when it has not be activated by water, and regardless of the water ph/CaC03 fresh promix will buffer to 6.2ish in 10 days due to the lime. If you transplant into fresh promix you can experience PH fluctuations for a few days, which is one of the main reasons I actually did this test.

The old promix you can see that the buffer is mostly gone as it no longer maintains at 6.2ph at 10days. and that water Alkalinity can have a more dramatic influence on PH in used up promix with no left over lime. I was expecting to see lower ph numbers due to the peat moss. but the alkalinity in the water seems to have buffered the PH to stay in the 6s showing the impact of alkalinity at 160PPm.

Click to expand...

So I use flora micro grow bloom. I still have to test alkalinity of my nutrient solution. But if it’s quite high I guess it would benefit from some ph down correct?

Tommy125 said:

So I use flora micro grow bloom. I still have to test alkalinity of my nutrient solution. But if it’s quite high I guess it would benefit from some ph down correct?

Click to expand...

Just checked half strength bloom nutes at 430 ppm. With no ph down, ph went to 6.6 and alkalinity did not change much. Is it safe to say I don’t need ph down?

Tommy125 said:

Just checked half strength bloom nutes at 430 ppm. With no ph down, ph went to 6.6 and alkalinity did not change much. Is it safe to say I don’t need ph down?

Click to expand...

yah I have never had to use ph down for my crop personally with promix. I find with my water/nutrients and the amount of times i transplant keeps my ph good (runoff) throughout my runs. Ive heard only very expensive probe meters are trustworthy like the blue lab ones to my understanding and personally im to cheap for that, i have the cheapo vivosun ppm/ph meters for like 25-30$ and i cross referenced them against ph drops and the water analysis for my city and a 2nd ph/ppm meter i have.

May I ask how you are testing water alkalinity? I have seen water droplet tests for it but never really looked into it.

Check this out for medium testing

The promix rep is right, those saying buy a soil meter and use ph up and down are wrong.

In a high calcitic ppm water acid can nutralise the calcium the same way the lime in soil buffers the acid. A simple water report available online from your water company will confirm alkalinity and calcium content and let you know that the water is ok or far too high in ppms.

Its a canna site, too many think water sets your soil ph that you wont get a straight answer.

Tommy125 said:

Hi how do you correct ph of the medium. The promix representatives say you cannot change the ph of the medium with ph up or down?

Click to expand...

kingkush4200 said:

yah I have never had to use ph down for my crop personally with promix. I find with my water/nutrients and the amount of times i transplant keeps my ph good (runoff) throughout my runs. Ive heard only very expensive probe meters are trustworthy like the blue lab ones to my understanding and personally im to cheap for that, i have the cheapo vivosun ppm/ph meters for like 25-30$ and i cross referenced them against ph drops and the water analysis for my city and a 2nd ph/ppm meter i have.

May I ask how you are testing water alkalinity? I have seen water droplet tests for it but never really looked into it.

Check this out for medium testing

Media and Tissue Testing - Measuring pH and E.C. of Media | PT Growers and Consumers

Manage the pH and electrical conductivity of your growing substrates! Discover efficient and precise analysis methods for optimal growth.

www.pthorticulture.com

Click to expand...

Is the meter you use a soil probe? I just tested today with a pool test strip kit, it measures total alkalinity. The colours are pretty distinct but it is only approximate.

2Hearts said:

The promix rep is right, those saying buy a soil meter and use ph up and down are wrong.

In a high calcitic ppm water acid can nutralise the calcium the same way the lime in soil buffers the acid. A simple water report available online from your water company will confirm alkalinity and calcium content and let you know that the water is ok or far too high in ppms.

Its a canna site, too many think water sets your soil ph that you wont get a straight answer.

Click to expand...

Thank you. I am on a well so no city water. My water is 8.2 ph 125 ppm and between 40-80 ppm alkalinity. I’m thinking I don’t need to use ph down. Would you agree?