The Cal-Mag of my dreams?

[Steve Johnson]

It's like I'm back in school.

Right there with you -- and sometimes I feel like I'll never graduate!

Would be good to know before I start testing my watering solution and eventually the run-off of my soil mix, also 60% pumice : 40% gravel mix. Although I add diatomaceous earth (powder form). I would be testing after each step and the order is now:
1) tap water (1l)
2) acidify (viewtopic.php?t=43525&start=45)
3) fertilizer (0,92 ml GHE FloraMicro + 0,92 ml GHE FloraBloom)
4) potassium sulfate (38,8 ml potassium sulfate stock solution (1,84 gr/l))

Wrong order. It should be:
1) Tap water.
2) Fertilizer and Potassium sulfate stock solution in the amounts you just specified.
3) Diatomaceous earth in whatever amount you're using. By the way, why are you using it?
4) Test the pH of the runoff water (that's the "slurry test" I described in my acidification how-to thread).
5) Add a small amount of the acidifier you'll go with (either 5% white vinegar or citric acid, take your pick), then test the final pH.
Your target pH range should be 5.0-5.5. If it's above 5.5, add a smaller amount in increments until you hit the target. If it goes below 5.0, dump out the watering solution and start all over again. Hint: The acidifier always goes in last for the testing process. Once you determine the correct amount that hits your target, write it down and tape it to your watering container so you don't forget. Since the pH of tap water may tend to fluctuate, I highly recommend that you test your watering solution every month or two in case you'll need to adjust the amount of acidifier. If you ever change your mix (or use different mixes for different species), you'll need to run the "slurry test" again. If you don't, you're set.

I realize all this is "labor-intensive", but as I said earlier, those of us who aren't so casual about optimizing the growing quality of our cacti over the years won't mind taking the time to do it properly.

I didn't exactly excel at math and chemistry back in the day.

I'm right there with you too. Hopefully someone with better math and chemistry skills (think that'll be Jerry) will interpret the water quality data you and I have posted.

[ohugal]

Ok. Thanks for the correction. I think the time spent researching and writing on the topic almost outweighs the actual process of treating the water.
Misunderstanding regarding the D.E., I add it to my soil mix, not the water. In it's dry state it discourages (or is supposed to) root mealies. I never had them so far. Though I can not prove it's becaus of the D.E..
So to be clear:
1. Tap water
2. Add fertilizer + potassium sulfate.
3. Water substrate in question with mixture and capture runoff.
4. Test pH of runoff.
5. Add acidifier to runoff and test pH again.
6. If necessary, adjust acidifier en repeat process.

Regarding the water, it's not clear to me how to interpret to numbers. I know the water is neither hard, nor soft, so I assume it's not going to be a huge issue. If I test my watering solution and runoff for carbonate and general hardness I just need to know what to look for. I try to keep up, but a lot of information here (as we say in dutch) 'gaat mijn petje te boven'. (https://www.deepl.com/translator#nl/en/ ... te%20boven.)

[keith]

MikeinOZ

The others just get Gypsum. About 1/2 gram per 10cm pot. Things like Epithelantha and Ariocarpus get gypsum and a large amount of limestone ''sand'' (<>1mm particles). As much as a teaspoon for a 10cm pot and they are growing well with that."

Ok I get it Limestone sand and Gypsum for extra Calcium and I expect the limestone to last forever improving drainage and giving off tiny amounts of calcium. Gypsum I guess more of a somewhat soluble source of CA and sulfur. You use a organic base soil if I remember right ? your own compost ?

I used to use dolomite long ago for Ariocarpus because Powdered limestone for cement is no good.

[jerrytheplater]

Steve's questions about his water test report:

This brings up 3 questions, and the answers should be able to guide me on what to do when I start using the GH ferts:

Does the 7.0 pH coming out of my tap mean that the hardness of my water is entirely permanent? Using the Avg Diemer plant results since I don't know which plant serves Steve: Total Hardness avg over the year is 274 ppm. Alkalinity is 125 ppm. 274 - 125 = 149 ppm Hardness due to Ca and Mg and any trace divalent cations. That is your permanent hardness, or hardness that will not be removed by acidification/boiling.

If so, can my cacti take up the Ca and Mg in the acidified tap water? You acidify your water with vinegar. That is dilute Acetic Acid (5-7% I think). You will be converting your Ca and Mg from bicarbonates to acetates as you lower the pH. They are water soluble. Your plants should easily be able to use them. By the way, they are also soluble at pH 7.0 as bicarbonates.

If the answer to question #2 is "yes", would the plants still benefit from adding the TPS CalMag to the GH ferts? Using #1 concentration of 149 ppm Hardness due to Ca and Mg Carbonates (in real life, they exist as bicarbonates at your pH 7.0-they are reported as Carbonates for the testing and calculations.), yes to adding more CalMag to your fertilizer. Not all of that 149 ppm is Ca/Mg-there are the bicarbonates that are there as well that go into that weight. I really don't want to calculate it now, and it really does not matter. You will be watering with an excess of Ca/Mg and other nutrients. They will drain through. The plants will take up what they can like they are already.

Order of mixing up the batch of fertilizer for Ohugal:

Ohugal wrote he would acidify his water first. Steve answered he would not. My first reaction is to acidify first, but I want to understand why Steve answered like he did.

Steve, can you save me the time of searching your acidifying post and let me know what "runoff water, as in "plenty of runoff water for testing " and "slurry test" are? I am trying to see what you are saying about pH rebound: what you did and what you got. Links? Save me the search please. Date of the post?

Order of GH fertilizer additions are clearly posted on the GH website. I'd follow it exactly. Add Micro first (pH 5. to your water and then Bloom (pH 3.5). They specify this so you are diluting the Calcium in the Micro before adding the Phosphate in the Bloom. Otherwise you could precipitate Calcium Phosphate in your mix. Try adding equal amounts of undiluted Bloom and Micro in a clear container, shake/stir well, and look through the solution against a black background. You will see a white cloudiness forming.

[jerrytheplater]

Ok. Thanks for the correction. I think the time spent researching and writing on the topic almost outweighs the actual process of treating the water.
Misunderstanding regarding the D.E., I add it to my soil mix, not the water. In it's dry state it discourages (or is supposed to) root mealies. I never had them so far. Though I can not prove it's becaus of the D.E..
So to be clear:
1. Tap water
2. Add fertilizer + potassium sulfate.
3. Water substrate in question with mixture and capture runoff.
4. Test pH of runoff.
5. Add acidifier to runoff and test pH again.
6. If necessary, adjust acidifier en repeat process.

Regarding the water, it's not clear to me how to interpret to numbers. I know the water is neither hard, nor soft, so I assume it's not going to be a huge issue. If I test my watering solution and runoff for carbonate and general hardness I just need to know what to look for. I try to keep up, but a lot of information here (as we say in dutch) 'gaat mijn petje te boven'. (https://www.deepl.com/translator#nl/en/ ... te%20boven.)

We might say in English, "That is above my pay grade". Ha Ha.

I meant to get to your questions regarding interpreting your test results. But I got involved in answering Steve and then went for a walk with the wife in the rain. Now I need to get on my Indoor Rower before I eat or else I don't row today. Your results seem to be in degrees of hardness and it looks like you are showing French, German, and English values. These numbers are all interconvertible, its just like fertilizer labels, each country has a different way of reporting test results.

And, as I asked Steve, I want to know more about this testing of run off water in the acidification process. I need to read what was written and think about it. Something is not sounding right to me, but I want to read it for myself.

Time to row. Happy New Year. I'll try and check later, but won't give a promise. Monday is another day.

[Steve Johnson]

Ok. Thanks for the correction. I think the time spent researching and writing on the topic almost outweighs the actual process of treating the water.
Misunderstanding regarding the D.E., I add it to my soil mix, not the water. In it's dry state it discourages (or is supposed to) root mealies. I never had them so far. Though I can not prove it's becaus of the D.E..
So to be clear:
1. Tap water
2. Add fertilizer + potassium sulfate.
3. Water substrate in question with mixture and capture runoff.
4. Test pH of runoff.
5. Add acidifier to runoff and test pH again.
6. If necessary, adjust acidifier en repeat process.

Yes, those are the correct steps for the testing process. The reason for going soil-less is that open aeration in the mix gives my cacti the ability to fully exploit vigorous root growth. Any type of fine material getting into the air spaces defeats the purpose unless it's absolutely necessary. In my case, I have 4 cacti with roots that can't be supported in a soil-less mix, but they do remarkably well in a 50/50 pumice and soil mix. For growers living in an arid climate, a certain amount of soil in the mix is required for adequate water retention. Here in the US, cactus growers contending with root mealy problems can eliminate them through Imidacloprid soil soaks in the growing season. However, you don't have that luxury in Europe, so DE might be a good preventative against root mealies. Unfortunately I can't tell you whether it is or not since I've never found a use for it.

[MikeInOz]

MikeinOZ
You use a organic base soil if I remember right ? your own compost ?

Not organic ''based'' but does always contain some well matured compost. Probably about 20 % for the desert types and more for the ''forest'' and grassland types. I also use some sphagnum peat to regulate the pH. Recently I got a few bags of kanuma and akadama which are both slightly acidic so I can leave out the peat in that case.

[MikeInOz]

"Steve Johnson"

Testing the runoff water, it rebounded up to 7.0 after 6 days.

That means you have a quantity of solid (probably calcium) carbonate in the media and regardless of the amount of acid you use, you will never permanently acidify the medium until all of the CaCo3 has been dissolved. The smaller the particles the faster the buffering back to what it was.
But, in the meantime, the acidified water will allow the cacti to take up the various nutrients they require. Therefore, acidify your water to the preferred range and don't worry about the CaCo3 in the mix - unless they are cacti which definitely prefer acid soil. It will be dangerous to try to compensate for the kind of buffering you are seeing by adding more acid!

[Steve Johnson]

Hi Jerry,

Thank you for your detailed responses -- we're blessed to have you and Mike on the forum.

Your answer to question #3 is intriguing:

If the answer to question #2 is "yes", would the plants still benefit from adding the TPS CalMag to the GH ferts? Using #1 concentration of 149 ppm Hardness due to Ca and Mg Carbonates (in real life, they exist as bicarbonates at your pH 7.0-they are reported as Carbonates for the testing and calculations.), yes to adding more CalMag to your fertilizer. Not all of that 149 ppm is Ca/Mg-there are the bicarbonates that are there as well that go into that weight. I really don't want to calculate it now, and it really does not matter. You will be watering with an excess of Ca/Mg and other nutrients. They will drain through. The plants will take up what they can like they are already.

That last comment confirms what I've intuitively believed. It also confirms that I really do need to flush my pots once a year. Should I do that in the spring or summer? Probably doesn't matter as long as I make it a regular part of my practice. When I flushed the pots a few years ago, I used distilled water, although my feeling is that acidified water may be better. (And yes, my acidifier is 5% white vinegar.)

Steve, can you save me the time of searching your acidifying post and let me know what "runoff water, as in "plenty of runoff water for testing " and "slurry test" are?

"Runoff water" means water coming down out of the pot when you saturate the mix. By the way, I should mention that when I did it in 2019, I was saturating a potful of my pumice-granite gravel mix to get runoff water without a plant in it. "Plenty of runoff water for testing" means having enough to test with a pH meter. Of course the soil-less mix isn't dust-free, and dirty brown runoff water indicated a significant amount of particulates draining through. Didn't want them to screw up the electrode on my Milwaukee Instruments pH 600, so I filtered the runoff water with a coffee filter first. A tupperware container full of clean runoff water was quite sufficient for the test. Calling it a "slurry test" may not be technically accurate, so maybe I should call it a runoff test instead.

I am trying to see what you are saying about pH rebound: what you did and what you got. Links? Save me the search please. Date of the post?

I never posted the details on my pH rebound test because I didn't think they would be relevant to anyone but me. Here's the process I followed:

• I always start by filling a jam jar with tap water, then test the reading on my pH 600. I have another jam jar filled with 7.0 reference solution at the ready -- if the meter isn't reading 7.0, I calibrate it with a jeweler's screwdriver that came with the meter. Once I get a steady 7.0 reading, I'm ready.

• Don't remember the exact date, but I ran the runoff test maybe a month or two before I posted my acidification "how to" thread on 9/8/2019. Following the above procedure, I took a reading before I saturated the mix -- pH of the acidified watering solution 5.5. Immediately after I filtered out the runoff water, I got a reading of 6.1. That's how I knew my soil-less mix is slightly (maybe not so slightly?) alkaline.

• Following the above procedure again, I ran a daily test, got the reading each day, and that's how I got a reading of 7.0 after 6 days.

Here is the pH 600:



As you can see, I was only able to test pH rebound in the runoff water, so I didn't have any way of testing the pH in the mix as it was drying out over those 6 days. Was my test accurate enough to be useful? Jerry, I'll let you decide.

What about the meter itself? I learned a lot from Darryl Craig of CoronaCactus Nursery back in 2012 when he was still on the forum, and he said that a pH meter is the only way to go. With many years of experience calibrating measuring instruments on microscopes, I knew that instruments which can't be calibrated are pretty much useless. As I searched out pH meters online, the only calibratable pen-style meter I found was the Milwaukee Instruments pH 600. It may not be the only game in town anymore, so for those of you who'd like to use a pen-style pH meter, make sure that you get one you can calibrate.

"Steve Johnson"

Testing the runoff water, it rebounded up to 7.0 after 6 days.

That means you have a quantity of solid (probably calcium) carbonate in the media and regardless of the amount of acid you use, you will never permanently acidify the medium until all of the CaCo3 has been dissolved. The smaller the particles the faster the buffering back to what it was.
But, in the meantime, the acidified water will allow the cacti to take up the various nutrients they require. Therefore, acidify your water to the preferred range and don't worry about the CaCo3 in the mix - unless they are cacti which definitely prefer acid soil. It will be dangerous to try to compensate for the kind of buffering you are seeing by adding more acid!

Agreed, and I'm pleasantly surprised by the fact that I don't have to add as much vinegar to the watering solution these days. Used to be 1 tbsp. per gallon as I mentioned, then down to 1 tsp. per gallon once I discovered that I had been accidentally over-acidifying. Maybe the runoff test was just an academic exercise anyway, but it doesn't change my need for being more diligent about periodically testing the acidified water.

[jerrytheplater]

Hi Jerry,

Thank you for your detailed responses -- we're blessed to have you and Mike on the forum.

Your answer to question #3 is intriguing:

If the answer to question #2 is "yes", would the plants still benefit from adding the TPS CalMag to the GH ferts? Using #1 concentration of 149 ppm Hardness due to Ca and Mg Carbonates (in real life, they exist as bicarbonates at your pH 7.0-they are reported as Carbonates for the testing and calculations.), yes to adding more CalMag to your fertilizer. Not all of that 149 ppm is Ca/Mg-there are the bicarbonates that are there as well that go into that weight. I really don't want to calculate it now, and it really does not matter. You will be watering with an excess of Ca/Mg and other nutrients. They will drain through. The plants will take up what they can like they are already.

That last comment confirms what I've intuitively believed. It also confirms that I really do need to flush my pots once a year. Should I do that in the spring or summer? Probably doesn't matter as long as I make it a regular part of my practice. When I flushed the pots a few years ago, I used distilled water, although my feeling is that acidified water may be better. (And yes, my acidifier is 5% white vinegar.)

Steve, can you save me the time of searching your acidifying post and let me know what "runoff water, as in "plenty of runoff water for testing " and "slurry test" are?

"Runoff water" means water coming down out of the pot when you saturate the mix. By the way, I should mention that when I did it in 2019, I was saturating a potful of my pumice-granite gravel mix to get runoff water without a plant in it. "Plenty of runoff water for testing" means having enough to test with a pH meter. Of course the soil-less mix isn't dust-free, and dirty brown runoff water indicated a significant amount of particulates draining through. Didn't want them to screw up the electrode on my Milwaukee Instruments pH 600, so I filtered the runoff water with a coffee filter first. A tupperware container full of clean runoff water was quite sufficient for the test. Calling it a "slurry test" may not be technically accurate, so maybe I should call it a runoff test instead.

I am trying to see what you are saying about pH rebound: what you did and what you got. Links? Save me the search please. Date of the post?

I never posted the details on my pH rebound test because I didn't think they would be relevant to anyone but me. Here's the process I followed:

• I always start by filling a jam jar with tap water, then test the reading on my pH 600. I have another jam jar filled with 7.0 reference solution at the ready -- if the meter isn't reading 7.0, I calibrate it with a jeweler's screwdriver that came with the meter. Once I get a steady 7.0 reading, I'm ready.

• Don't remember the exact date, but I ran the runoff test maybe a month or two before I posted my acidification "how to" thread on 9/8/2019. Following the above procedure, I took a reading immediately after I filtered out the runoff water. That's how I got a reading of 5.5.

• Following the above procedure again, I ran a daily test, got the reading each day, and that's how I got a reading of 7.0 after 6 days.

Here is the pH 600:



As you can see, I was only able to test pH rebound in the runoff water, so I didn't have any way of testing the pH in the mix as it was drying out over those 6 days. Was my test accurate enough to be useful? Jerry, I'll let you decide.

What about the meter itself? I learned a lot from Darryl Craig of CoronaCactus Nursery back in 2012 when he was still on the forum, and he said that a pH meter is the only way to go. With many years of experience calibrating measuring instruments on microscopes, I knew that instruments which can't be calibrated are pretty much useless. As I searched out pH meters online, the only calibratable pen-style meter I found was the Milwaukee Instruments pH 600. It may not be the only game in town anymore, so for those of you who'd like to use a pen-style pH meter, make sure that you get one you can calibrate.

"Steve Johnson"

Testing the runoff water, it rebounded up to 7.0 after 6 days.

That means you have a quantity of solid (probably calcium) carbonate in the media and regardless of the amount of acid you use, you will never permanently acidify the medium until all of the CaCo3 has been dissolved. The smaller the particles the faster the buffering back to what it was.
But, in the meantime, the acidified water will allow the cacti to take up the various nutrients they require. Therefore, acidify your water to the preferred range and don't worry about the CaCo3 in the mix - unless they are cacti which definitely prefer acid soil. It will be dangerous to try to compensate for the kind of buffering you are seeing by adding more acid!

Agreed, and I'm pleasantly surprised by the fact that I don't have to add as much vinegar to the watering solution these days. Used to be 1 tbsp. per gallon as I mentioned, then down to 1 tsp. per gallon once I discovered that I had been accidentally over-acidifying. Maybe the runoff test was just an academic exercise anyway, but it doesn't change my need for being more diligent about periodically testing the acidified water.

I went and opened this thread and can't think on it now till Monday. I will have to remember where it is. Wish there was a way to mark threads as unread. Happy New Year.

[Steve Johnson]

Wish there was a way to mark threads as unread. Happy New Year.

That is one small drawback to the way the forum is set up. Happy New Year to you as well!

[ohugal]

Happy New Year everyone!

I don't think I will add limestone or gypsum to my substrate, simply because I already have so many components in storage and my free space is running out. I do follow the discussion with interest though.

Jerry, in your responses to Steve's questions things became a bit clearer. Total hardness (in ppm) - alkalinity (in ppm) = permanent hardness (in ppm). I'm going to try find how to convert or obtain these numbers from the data available to me. Do not feel pressured to answer each and every one my questions. I also think the basic set-up we have here is pretty good.

I add my acidifier first because it seems like a logical first step. It's the basis for everything else. Also, here it would good to know if the order is important. To honest, I didn't know to add Micro first and then Bloom. Luckily it is in that order in my notes.

Steve, I do have a systemic at my disposal since recently (Perfekthion from BASF). I might use it. Imidacloprid is indeed not available to me. Acetamiprid (Carea from Celaflor) is, but I have used it but does not seem be effective. It is intended from spraying, not for soil soaks. It can be used for soil soaks at a higher concentration, but in that way becomes very expensive.

I have a good pH-meter from Hannah instruments. I will also test the rebound after 7 days. Is it an idea to soak the soil in the watering solution for an x-amount of hours, strain it and then measure? Also, why not directly test the pH of the soil with a meter (if possible) or strips?

[Steve Johnson]

Happy New Year everyone!

Happy New Year to you too, ohugal!

I add my acidifier first because it seems like a logical first step. It's the basis for everything else. Also, here it would good to know if the order is important. To honest, I didn't know to add Micro first and then Bloom. Luckily it is in that order in my notes.

You could do it that way, and I suppose the order really doesn't matter -- the point is to get a final pH reading of the acidified watering solution right before you water your cacti. As I said earlier, if the pH of the water going into your plants is below 5.0, you've acidified too much.

I have a good pH-meter from Hannah instruments. I will also test the rebound after 7 days. Is it an idea to soak the soil in the watering solution for an x-amount of hours, strain it and then measure? Also, why not directly test the pH of the soil with a meter (if possible) or strips?

First of all, and to be more precise in my terminology -- what I'm calling a "slurry test" should be more accurately described as a runoff test. "Is it an idea to soak the soil in the watering solution for an x-amount of hours, strain it and then measure?" Good idea for soil-based mixes, but we get instant results in a soil-less mineral mix. I tried that with my pumice and granite gravel mix -- 6.1 in the runoff water right after saturation, 6.1 after saturating again 2 hours later. "Also, why not directly test the pH of the soil with a meter (if possible) or strips?" Fair question, although I don't know how that can be done in a soil-less mix. I've tried test strips coming from different sources when I test my acidified watering solution, and quite frankly I've found the results to be unreliable. However, that's just my experience, so your experience with them may be better.

This is a well-informed response from Mike -- and a cautionary tale about the danger of over-acidification:

"Steve Johnson"

Testing the runoff water, it rebounded up to 7.0 after 6 days.

That means you have a quantity of solid (probably calcium) carbonate in the media and regardless of the amount of acid you use, you will never permanently acidify the medium until all of the CaCo3 has been dissolved. The smaller the particles the faster the buffering back to what it was.
But, in the meantime, the acidified water will allow the cacti to take up the various nutrients they require. Therefore, acidify your water to the preferred range and don't worry about the CaCo3 in the mix - unless they are cacti which definitely prefer acid soil. It will be dangerous to try to compensate for the kind of buffering you are seeing by adding more acid!

In my case I over-acidified accidentally, but I corrected the error. We certainly want to avoid doing it on purpose.

[jerrytheplater]

Well, its been more than a day! But I have been reading the acidification thread Steve has as a sticky and see that is where the terms runoff water and slurry test etc come from. I also saw the link to the 2008 article "Cactus and Alkalinity" by Elton Roberts and Malcom Burleigh. Not finished with it yet.

The proper way to test the pH of soils of whatever type is to take a good representative sample of the "soil" you want to test and place it in a clean non reactive container. Add enough Distilled Water to cover the sample by a few inches and stir well until everything is wetted. Let it soak for a few hours and then test the pH. If using electronic pH meters, you can place it in the water as long as you don't damage it by contacting the "soil". Filtering is acceptable. If using pH strips, (DaveW gave a link to a good quality pH strip in the acidification thread.) those strips should be kept in the solution being tested until there is no more color change-up to 10 minutes. If it is a strongly colored solution, the strip can be quickly rinsed off with DI water before reading.

Testing the water that runs out of a pot shows you what the effect of your potting mix has on your water you are using. If you are testing water containing fertilizer, the pH could change due to uptake by the plants as well as due to the effect of the potting mix itself. Letting the water soak the potting mix in a jar like I describe above gives a better idea of the effect of the potting mix because there will be time for reactions to occur.

Discard water if you drop the pH below 5.0? Didn't I read either in the Cactus and Alkalinity or the acidification thread the thunderstorms in the desert can acidify rainwater at times down to pH 3.5? Also, didn't I see that the pH of rain out West here in the US is much lower than in the East? If you went below 4.5 with vinegar, I would not be concerned.

I can give an example of pH adjustment from my waste treatment work pre retirement. At times I would have a 1200 gallon batch of very alkaline water containing large amounts of sodium carbonate and sodium hydroxide (pH greater than 13) that I would need to treat-it also contained dissolved metals that also needed removal. That water had hydroxide alkalinity, and carbonate alkalinity. I used concentrated sulfuric acid to lower the pH. The acid could be added quickly, 2.5 gallons at a time, without fear of violent fizzing until all of the hydroxide was neutralized at about pH 10.5.

At that point, acid had to be added slower to allow the CO2 to off gas, or else the tank would foam up and overflow. Also, that CO2 gas would give me an artificially lower pH than the solution would be if there was no CO2. I had to wait till I could get rid of all the CO2 gas by stirring to allow the pH to rise to a point where it stayed stable. Then I could get a true reading on the pH. The solution was heavily buffered by the bicarbonates and it took a lot of acid to remove it all.

I found that the carbonate/bicarbonate alkalinity would interfere with proper settling of the metal contained in that batch of wastewater in a later treatment step, so I would drop the pH down to below 3.0 to remove all of the alkalinity. This process could take a day or more. At that point I had zero alkalinity and would raise the pH back up to about 10.5 with Sodium Hydroxide. Still no carbonate/bicarbonate alkalinity. Then I would proceed with my regular waste treatment process.

[Steve Johnson]

Well, its been more than a day! But I have been reading the acidification thread Steve has as a sticky and see that is where the terms runoff water and slurry test etc come from. I also saw the link to the 2008 article "Cactus and Alkalinity" by Elton Roberts and Malcom Burleigh. Not finished with it yet.

While I'm grateful that I learned about the concept of acidification from Roberts' article, one of our members with a background in chemistry said that his knowledge of chemistry is suspect. Unfortunately I can't remember the source (this must've been from at least 10 years ago), but since you're a chemist, I'd be interested to get your take on this.

Discard water if you drop the pH below 5.0? Didn't I read either in the Cactus and Alkalinity or the acidification thread the thunderstorms in the desert can acidify rainwater at times down to pH 3.5? Also, didn't I see that the pH of rain out West here in the US is much lower than in the East? If you went below 4.5 with vinegar, I would not be concerned.

That was Roberts making the claim about thunderstorms in the desert acidifying rainwater down to pH 3.5. From knowledgeburrow.com:

"What kind of minerals are in alkaline soil?

Soil that is alkaline usually contains large amounts of calcium, sodium, and magnesium, and it is less soluble than acidic soil. Arid regions typically contain alkaline soil. [My emphasis]"

Habitat cacti in the open ground of their native alkaline soils are growing under conditions that are very different from growing cacti in pots under cultivation. Assuming that his claim is true, rainwater starting out with a pH of 3.5 in the ground will rebound up quickly until the soil reaches its dry alkaline state. My guess is just a few days for the roots to dry out. The pumice and granite gravel mix I use takes 7-8 days to dry out (believe or not, this is consistent drying behavior regardless of pot size). Now here's what I posted to the acidification "how to" thread in August 2020:

The tap water here in L.A. had been on the hard side for many years, my part of it fluctuating between a pH of 7.5 and 8 depending on the season (higher in the winter and summer). With periodic checks of my pH meter, I was keeping the final pH of my acidified water and fertilizer solution to a number in the 5-5.5 range using 1/2 tsp. Dyna-Gro 7-7-7 plus 2 or 2 1/2 tsp. of 5% vinegar. Then last summer I got lazy and decided that A. 2 tsp. of vinegar should be fine, and B. I didn't need to check the pH meter anymore. Just out of curiosity, I checked it at the beginning of this spring -- don't know when or why it happened, but our water quality improved as the pH coming out of my tap was an even 7.0. Add the Dyna-Gro and 2 tsp. of vinegar, and the final pH this time was 4.0.

4.0 -- eek! Factoring in 7 days of rebound time as the mix dried out, the pH of the residual moisture after 7 days was still way too low. My cacti looked really good in 2019, not so much in spring and early summer 2020 -- took awhile before I noticed the negative effects of over-acidification. Once I started keeping the acidified watering solution in the 5.0-5.5 range, they perked up faster than I would've imagined.

Jerry, your point about the proper way to test soil pH is well-taken, so I'll follow the procedure you described for a new test next month. In fact, it may not be a bad idea to do a "live fire" test with 1 gallon of watering solution which will include the right amounts of FloraMicro, FloraBloom, Potassium sulfate stock solution, and TPS CalMag. Anything that doesn't stay in the test container will go into a couple of plants that aren't cacti.

While we're here...

Those products you mention seem to be for hydroponics and have nitrate as the major N source. I believe I read that cacti prefer ammonium to nitrate so I'm not sure if they are the best option??

We had an expert grower by the name of iann who used to be active on the forum, so here's some food for thought:

So just this tiny insight into plant chemistry shows that Nitrate and Ammonium perform differently in the plant and each would be the best solution (sic) in different conditions. The hundreds of papers on this subject show the same thing. Different plants, or the same plant in different conditions, may take up one or other ion preferentially but are quite capable of doing it from a mix of available Nitrogen forms. In any case, they usually perform best when they are able to take up both forms. The rare benefits to applying just a preferred single form of Nitrogen (which can be either Nitrate or Ammonium) are far outweighed by the dramatically poor performance in most cases of applying only the "wrong" single form. If you want to start an interesting chain of thought in this context, it is worth noting that one consistent trend is for plants to prefer Ammonium ions in more acidic conditions and Nitrate ions in less acidic conditions. Another is that Nitrate ions tend to be preferred in hotter conditions.

A couple of things come to mind:

• Since hydroponic fert manufacturers seem to tilt heavily in favor of Nitrate N, they may know something we don't.

• Iann's last statement suggests that desert cacti in the wild prefer Nitrate. Either that or it's their only significant soil-based Nitrogen source.

You can take the cactus out of the desert, but can you take the desert out of the cactus? Just a theory -- generations of desert species seed-grown in nurseries share the same genetic heritage as their wild counterparts, so it stands to reason that desert cacti under cultivation do prefer Nitrate N in the ferts they get. This could be an interesting subject for debate -- please feel free to discuss it here if you're so inclined!