The Cal-Mag of my dreams?

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Steve Johnson
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Re: The Cal-Mag of my dreams?

Post by Steve Johnson »

While everyone is waiting, I have a little something for those of you who may be confused about alkalinity and hardness. From the University of Utah Extension's online water quality article:
  • Alkalinity and Hardness

    WHAT IS ALKALINITY?

    Alkalinity is water's capacity to resist acidic changes in pH, essentially alkalinity is water's ability to neutralize acid. This ability is referred to as a buffering capacity. A water body with a high level of alkalinity (which is different than an alkaline water body) has higher levels of calcium carbonate, CaCO3, which can decrease the water's acidity. Therefore, alkalinity measures how much acid can be added to a water body before a large pH change occurs.

    ALKALINITY VS WATER HARDNESS

    Alkalinity and water hardness are fairly similar--essentially they both come from sources in nature. Water moves through rocks (and picks up minerals as it does so) on its way to rivers and lakes. When limestone and dolomite dissolve in water, one half of the molecule is calcium or magnesium (the "hardness") and the other half is the carbonate (the "alkalinity"). This means that the level of water hardness and alkalinity in a place will be very similar. However, they are very separate measurements, and have very different importance.
Source: https://extension.usu.edu/waterquality/ ... alkalinity

If you're acidifying your tap or well water, here's a note from Jenco (https://blog.jencoi.com/what-is-ph-in-water-testing):
  • Water Testing With a pH Meter

    A pH meter provides a much more accurate reading than a test strip kit and prevents the mess associated with having to use droppers. Calibration before testing water samples ensures that the pH meter will provide accurate readings and test results.
Although I still rely on the Milwaukee Instruments pH 600 I selected 11 years ago, it's not the only game in town anymore, so make sure that you buy a pH meter you can calibrate.
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Steve Johnson
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Re: The Cal-Mag of my dreams?

Post by Steve Johnson »

MrXeric wrote: Sat Feb 04, 2023 11:55 pm I'm not a chemist, just familiar with the basic principles at the undergraduate level, but calcium bicarbonate exists only as aqueous solution in the form of [Ca]2+ and [HCO3]- ions in water, in equilibrium with dissolved CO2 and carbonate ions. Similar to aqueous sodium bicarbonate, the acid part in acetic acid will react with the bicarbonate (and carbonate) to produce CO2 and water, leaving you with calcium and acetate in ionic form that will crystallize when dry as calcium acetate.
jerrytheplater wrote: Sun Feb 05, 2023 1:07 amCalcium bicarbonate and Calcium Carbonate will react very similarly with acetic acid. Both will produce Calcium acetate. If you want a balanced equation, I could probably do it, but you really don't need it in my opinion. I doubt you are calculating concentrations etc.
I'm glad you guys chimed in because I didn't get an answer from Quora yet.

As MrXeric said, calcium bicarbonate exists only as an aqueous solution, and I was interested by what Jerry just said -- "Calcium bicarbonate and Calcium Carbonate will react very similarly with acetic acid" [my emphasis]. When hard water evaporates, water vapor and CO2 are released into the atmosphere, which leaves only calcium carbonate (CaCO3) as a solid in the pot. If you've ever seen white stuff around the outside of a porous terracotta pot, that's the visible CaCO3 product of evaporation in hard water. Problem is that calcium carbonate is insoluble, "locking up" calcium which makes it unavailable to the plant. But when the acetic acid in vinegar reacts with calcium bicarbonate and carbonate in water, we get calcium acetate which is highly soluble -- this makes calcium available to the plant when you water. Because there's no such thing as too much calcium (at least for cacti), calcium acetate gives us and them an additional source of calcium they can use -- a source denied to them by insoluble CaCO3.

Before we continue, I'll admit that I made a bad assumption regarding alkalinity in the pumice component of my hydroponic pumice and granite gravel mix. From the Wikipedia article on pumice (https://en.wikipedia.org/wiki/Pumice):

"With regard to chemical properties pumice is pH neutral, it is not acidic or alkaline."

Okay, that's settled -- since I know that the hydroponic mix is in fact pH-neutral, all I'm concerned about now is dealing with the hardness of my tap water. After seeing it with a pH fluctuating between 7.5 and 8 for 8 years, the water had been showing a pH of 7.0 for the last 2. I tested again last month, and now it's showing 7.3. Since the hardness is back, I'll have to start periodically testing the tap water again. If it tests at 7.0, there's no need to acidify. Anything above 7, and I'll have to get a pH reading as I determine how much vinegar I should add. Rule of thumb here in SoCal -- tap water pH is lower in spring and fall than it is in winter and summer, so I'll have to keep that in mind for periodic testing.

When acidified water is applied to the plant, pH rebounds up as the vinegar-bicarbonate/carbonate reaction slowly wears off. If the rebound hits a pH of 7.0 and stays there, neutralization is complete. However, if the rebound climbs back up above 7, neutralization is only partial -- and evaporation of the remaining water leaves calcium carbonate behind in the pot. Ideally we would like to get complete neutralization of bicarbonate and carbonate by the time the potting medium dries out from top to bottom, but here's where acidification does have its limits:

pH_nutrient_ availability_ chart04.jpg
pH_nutrient_ availability_ chart04.jpg (83.12 KiB) Viewed 1020 times
On the lower end of the pH scale, the red boxes show where nutrient leaching causes a significant reduction of N, P, K, S, Ca, and Mg available to the plant. I'm including Mo because we don't want too much leaching of the Sodium molybdate supplement before it gets into the plant for Nitrate-ammonium conversion. In order to maximize availability of all nutrients, I'd suggest that acidification of hard water in a watering solution should be no lower than 6.0. If you're adding dilute fertilizer and any fert supplements you may be using, check the watering solution's pH before you add the vinegar -- a final pH of 6.0 for the watering solution is your target.

The issue of pH rebound levels over time is important, so I'll run a test that's a lot simpler than the procedure I described in my February 3 post:

1. Fill a 1-gallon jug halfway up with tap water. Add 1/2 tsp. Dyna-Gro 7-7-7, 5 fluid ounce Potassium sulfate stock solution, 1/4 tsp. TPS CalMag, and 2 tsp. Sodium molybdate stock solution. Fill the jug all the way up to the fill line. Test the pH and write down the number.

2. Add 1/8 tsp. 5% white vinegar, cap the jug, shake well, then pour some of the water out into a jam jar and test the pH. This does take some patience because I'll have to "sneak up" on the target pH of 6.0. Pour the water back into the jug, continue adding vinegar in 1/8 tsp. increments, and test the sample of each increment until I hit the target. I'll write down the total amount of the vinegar I added.

3. Pour some of the watering solution into a large container and put a lid on it to prevent evaporation during the test.

4. Wait for 7 days, take off the container's lid, and test the pH of the water. Write the number down.

After 7 days of rebound, I'll know if neutralization is complete or partial. If it's complete at the 7-day mark, pH between 6.5 and 7 is quite acceptable to the cacti. Whether or not rebound creeps up any higher will depend entirely on what I get when the test is done. Can't come to any conclusions until I get the results, so we'll have to see what happens.

Although I may be in the minority, I'm by no means the only one growing cacti in a soil-less mix. Unfortunately the only soil-less mix I have direct experience with is the pH-neutral hydroponic mix, so growers using other soil-less mixes will need to test the pH of their mixes before they determine if acidifying hard water is required. If I remember correctly, I think Jerry came up with a good testing procedure, but it's buried in with a lot of other posts, so lotsa luck trying to find it again. I'm sure we can come up with something that'll work. For people growing cacti in soil-based mixes, use a pH soil tester.

Going back to the acidification "how to" guide I posted in 2019, there's much I didn't know then, so I think it'll need to be seriously revamped. In the meantime...

The word "acetate" sticks in my mind because one of our veteran members by the name of iann used to bring it up. While I was about to end here, I went to Advanced search, typed in "acetate" and "iann", and found the following item for you:
iann wrote: Mon Dec 06, 2010 4:08 pm There's very little difference between the deposits left by acetic acid or citric acid. Calcium acetate is highly soluble and calcium citrate is soluble enough that it shouldn't matter at the concentrations you'll be using. The carbonate byproducts are exactly the same. I'm not sure about the speed of the reactions, but it is likely to depend far more on the pH than on the exact acid being used.
This is really good -- if your collection is too large to make vinegar feasible, citric acid is stronger but safe for home use. And guess what? Calcium citrate is another source of calcium available to cacti.
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MikeInOz
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Re: The Cal-Mag of my dreams?

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Hi Steve, I was looking at some forums re using vinegar for pH adjustment and found this...

''Sorry folks, vinegar is not really the best thing for dropping pH, at least not in hydro systems. It is a product of fermentation and the only thing that keeps it from fermenting further in the bottle is the acid content. Dilute it and it can begin to ferment again. You can test this by putting some vinegar in clean, sterile water (non-chlorinated) in a sealed jar at room temp. Check this in 3-4 days; you will likely see some gelatinous gack forming in the water.
pHDown is one of the very cheapest sauces in a hydro shop, a few bucks a litre. Too cheap to use substitutes that have the potential to cause probs''. .


I have never used vinegar so I don't really know but it is not used in commercial hydro set ups as far as I know.
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Steve Johnson
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Re: The Cal-Mag of my dreams?

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MikeInOz wrote: Mon Feb 06, 2023 6:22 am Hi Steve, I was looking at some forums re using vinegar for pH adjustment and found this...

''Sorry folks, vinegar is not really the best thing for dropping pH, at least not in hydro systems. It is a product of fermentation and the only thing that keeps it from fermenting further in the bottle is the acid content. Dilute it and it can begin to ferment again. You can test this by putting some vinegar in clean, sterile water (non-chlorinated) in a sealed jar at room temp. Check this in 3-4 days; you will likely see some gelatinous gack forming in the water.
pHDown is one of the very cheapest sauces in a hydro shop, a few bucks a litre. Too cheap to use substitutes that have the potential to cause probs''. .


I have never used vinegar so I don't really know but it is not used in commercial hydro set ups as far as I know.
Hi Mike,

I've been successfully using vinegar for acidification since early 2012, so no problems at all. "Dilute it and it can begin to ferment again. You can test this by putting some vinegar in clean, sterile water (non-chlorinated) in a sealed jar at room temp. Check this in 3-4 days; you will likely see some gelatinous gack forming in the water" -- well, that's not what I'm doing. 2 tsp. per gallon of water, I'm watering my cacti right after, so we're looking at 130 ppm vinegar in the watering solution. No gelatinous gack with 130 ppm in a gallon of water.
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Re: The Cal-Mag of my dreams?

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Steve,

Just hypothesizing here, but let's say your fertilizer solution goes from pH 6 to a number over 7 in a very short period of time (e.g. 2 days). What could possibly be done about it? Also, do different acidifiers differ in the time they can keep the pH at a certain level? Are some more efficient then others?
I tested my cactus mix yesterday and came to a reading of pH 6. For the time being I did the test with distilled water and a Takemura soil tester. My soil is 4 grit : 5 pumice : 1 loam. Not completely on topic with this, but just wanted to share it anyway.
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Re: The Cal-Mag of my dreams?

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How to test the pH of a particulate sample (ie potting soil, sand, pumice, decomposed granite, poultry grit, peat moss, coir, etc. etc. etc.)

Place about an inch or so of your sample in a clean glass or plastic non reactive container. Fill with rain water, RO water, Distilled water to over an inch above the sample. Stir well so it is all wet. If something that resists getting wet like dry peat moss, you may have to wait a day or more till it is all wet. Stir periodically. Let it settle and test the pH of the liquid portion. No need to filter.

Just know that glass pH probes are very fragile. Don't press them into particulate solids. I broke one in my first Chem lab in college back in 1971 by just barely tapping it against the edge of the beaker as I was removing it from the beaker. It was $50.00 back then.

I know electronic pH probes exist which can dry out and be inserted directly into solids like food and soil without any danger. They are metallic. I once owned one at work. They are very handy. The one I had was not cheap. I have not looked at hobby pH measuring equipment recently, so can't give any advice.
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Re: The Cal-Mag of my dreams?

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ohugal wrote: Mon Feb 06, 2023 6:26 pm Steve,

Just hypothesizing here, but let's say your fertilizer solution goes from pH 6 to a number over 7 in a very short period of time (e.g. 2 days). What could possibly be done about it? Also, do different acidifiers differ in the time they can keep the pH at a certain level? Are some more efficient then others?
I tested my cactus mix yesterday and came to a reading of pH 6. For the time being I did the test with distilled water and a Takemura soil tester. My soil is 4 grit : 5 pumice : 1 loam. Not completely on topic with this, but just wanted to share it anyway.
First of all, Jerry has it right, so you did well by testing the pH of your mix with distilled water. Since it's reading with a pH of 6, acidity in the mix will neutralize bicarbonates and carbonates in the water to a certain extent. I seriously doubt that the pH would rebound up from 6 to 7 in 2 days, so actual rebound time is something you'll have to test in the pot, although best to do this with a cactus in it. When your growing season begins, give one of your test cacti a deep watering, measure the soil pH daily until right before the mix completely dries out top-to-bottom, and the final pH will tell you if acidification is advisable. Serious nutrient leaching with a pH below 5.0 is something we need to avoid, so if you do acidify, it'll have to be a very small amount. By the way, fertilizers tend to lower the pH of the water a little bit depending on the fert. The pH of your tap water gives you a benchmark, so test it and write down the number before you create a watering solution, Then when you fill your watering container with water, add the fert and any fert supplements you're using, shake well, test its pH and write that number down too. If your fert and supplements do in fact lower your tap water's pH a little, it's less likely that you'll need to acidify. Before you know whether or not you do, see what the pH is when your test pot's mix is about to dry out completely. If the pH is 7.0, that'll be good news -- you won't have a calcium carbonate buildup problem in your pots.

Regarding acidifiers, I think one acid is a good as another. The only difference I can see is in the concentration -- vinegar has a very low concentration of acetic acid. Great for a small collection like mine, but the amount of vinegar required isn't feasible for bigger collections, so citric acid is a better option -- more concentrated, yet safe for home use. Cactus nurseries use sulfuric or phosphoric acid, and they have to be used only by people who really know what they're doing.
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Re: The Cal-Mag of my dreams?

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jerrytheplater wrote: Mon Feb 06, 2023 7:52 pm How to test the pH of a particulate sample (ie potting soil, sand, pumice, decomposed granite, poultry grit, peat moss, coir, etc. etc. etc.)
Rather than taking Wikipedia's word for it, I'll test the pH of my pumice and gravel mix. Your testing instructions are straightforward, I have a plastic non-reactive container and a half-gallon of distilled water that could be put to good use, so I'll find out if the mix really is pH-neutral.
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Re: The Cal-Mag of my dreams?

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Steve Johnson wrote: Mon Feb 06, 2023 11:38 pm
jerrytheplater wrote: Mon Feb 06, 2023 7:52 pm How to test the pH of a particulate sample (ie potting soil, sand, pumice, decomposed granite, poultry grit, peat moss, coir, etc. etc. etc.)
Rather than taking Wikipedia's word for it, I'll test the pH of my pumice and gravel mix. Your testing instructions are straightforward, I have a plastic non-reactive container and a half-gallon of distilled water that could be put to good use, so I'll find out if the mix really is pH-neutral.
Great that you will test both. You know what happens when you ASSUME, I assume!

Did you see the Understanding Plant Nutrition links I put up here: https://cactiguide.com/forum/viewtopic.php?t=47623 ? I have not read them all yet, but in this one: Addressing Media pH Problems: Alkalinity and Nitrogen Forms: https://www.greenhousegrower.com/produc ... -problems/ , there is a quote "The form of nitrogen in your fertilizer is what causes substrate pH to decrease or increase." Its the plant roots absorbing NH4 that lowers media pH and absorbing NO3 that raise the media pH. Water Alkalinity can counteract this tendency.

What does all of this show me? That I have a lot to learn.
Jerry Smith
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Re: The Cal-Mag of my dreams?

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jerrytheplater wrote: Tue Feb 07, 2023 1:12 amDid you see the Understanding Plant Nutrition links I put up here: https://cactiguide.com/forum/viewtopic.php?t=47623 ? I have not read them all yet, but in this one: Addressing Media pH Problems: Alkalinity and Nitrogen Forms: https://www.greenhousegrower.com/produc ... -problems/ , there is a quote "The form of nitrogen in your fertilizer is what causes substrate pH to decrease or increase." Its the plant roots absorbing NH4 that lowers media pH and absorbing NO3 that raise the media pH. Water Alkalinity can counteract this tendency.

What does all of this show me? That I have a lot to learn.
I went through some of it, and all I learned is -- compared to growing crops, cacti are a lot easier. IMO those articles make things needlessly complicated, so I'll stick with what I've been learning from Mike.
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Re: The Cal-Mag of my dreams?

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Steve,
If you are using NZ pumice I've already tested it. It was 7.
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Re: The Cal-Mag of my dreams?

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MikeInOz wrote: Tue Feb 07, 2023 3:07 am Steve,
If you are using NZ pumice I've already tested it. It was 7.
Hi Mike,

I had been buying pumice from the California Cactus Center in Pasadena, but I don't know where they were getting it from. However, the chemical composition might tell us a little bit:

Chemical-composition-of-pumice.jpg
Chemical-composition-of-pumice.jpg (32.64 KiB) Viewed 943 times
No calcium or magnesium carbonate, so that's good. Now we'll look at the chemical composition of granite:

SiO2 72.04% (silica)
Al2O3 14.42% (alumina)
K2O 4.12%
Na2O 3.69%
CaO 1.82%
FeO 1.68%
Fe2O3 1.22%
MgO 0.71%
TiO2 0.30%
P2O5 0.12%
MnO 0.05%

No calcium or magnesium carbonate there either, but since I'm using granite gravel in the mix, I wanted to find out if any of the other chemical compounds react to water. I asked that question online, no answer, but here's a question that did give me an answer (from, oddly enough, answers.com): Does granite react to acid? No it does not. Igneous rocks in general rarely react with acid. And since water isn't acid, the granite gravel is pH-neutral too -- no need to test the pH of the hydroponic mix.
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Re: The Cal-Mag of my dreams?

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Steve, what's the big deal about testing your media pH? It might take all of 30 minutes, or you could wait overnight. Its the pumice I wonder about.

Yes, I expect the granite to be neutral. Your analysis for the granite is not for what is soluble/available, it is an actual analysis of the rock after extremely aggressive acidic digestion, probably even using perchloric acid. The pumice analysis is probably the same.

The reservoir which holds our water and the local rivers that feed it are travelling over granite and gneiss, and both are unreactive. Our water is very low in TDS.
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Re: The Cal-Mag of my dreams?

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jerrytheplater wrote: Tue Feb 07, 2023 4:54 am Steve, what's the big deal about testing your media pH? It might take all of 30 minutes, or you could wait overnight. Its the pumice I wonder about.
Here's the problem -- the Milwaukee Instruments pH 600's electrode is ruined in distilled water (says so right in the instructions), so I'd be taking a chance on having to buy a new meter if the pumice turns out to be pH-neutral. If I can test a pumice sample with tap water, that's easy -- test the pH of the tap water first, put some pumice into a clean jar, add tap water, and test the water in the jar an hour later. Is that okay?
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Re: The Cal-Mag of my dreams?

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Steve Johnson wrote: Tue Feb 07, 2023 5:27 am
jerrytheplater wrote: Tue Feb 07, 2023 4:54 am Steve, what's the big deal about testing your media pH? It might take all of 30 minutes, or you could wait overnight. Its the pumice I wonder about.
Here's the problem -- the Milwaukee Instruments pH 600's electrode is ruined in distilled water (says so right in the instructions), so I'd be taking a chance on having to buy a new meter if the pumice turns out to be pH-neutral. If I can test a pumice sample with tap water, that's easy -- test the pH of the tap water first, put some pumice into a clean jar, add tap water, and test the water in the jar an hour later. Is that okay?
If you are thinking that placing your probe in DI water that is covering the pumice for a few seconds while you take the reading will cause a problem, don't worry. It won't matter. It is soaking in DI water for prolonged periods that can ruin electrodes, like storing them for days. Rinsing with DI between readings to ensure you don't contaminate between multiple samples is perfectly fine. If you had to use tap water to rinse when you went between samples, you'd have problems of contamination of your samples.

Now I'm remembering a tip I read years ago when using Merck pH test strips. They said that some saturated KCl solution could be added to poorly buffered solutions to enable better pH readings-or something to that effect. That solution will have the pH of the DI water used to make it up. And it would probably be acidic due to dissolved CO2. But of such low strength that it would not affect pH readings in samples.

I didn't get out my book on rocks and minerals, but I remember there are different types of lava based on their pH reaction. Three maybe? Acid, neutral, basic. Also based on their flow characteristics. I have no idea if the solidified rock or pumice from those lava types have different pH reactions, but they could, and in my mind raise a doubt over assuming the pH of your pumice. This is why I press the issue.
Jerry Smith
Bloomingdale, NJ
45 inches (114 cm) rain equivalent per year, approx. evenly spread per month
2012 USDA Hardiness Zone 6b: -5F to OF (-20C to -18C) min.
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