The Cal-Mag of my dreams?

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jerrytheplater
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Re: The Cal-Mag of my dreams?

Post by jerrytheplater »

Take 2 times the molecular weight of potassium and divide by the molecular weight of potassium sulfate. That is about 44%. If you want the decimals, you'll have to look it up.

Sulfur is the same as above, except MW of S divided by MW K2SO4.
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Re: The Cal-Mag of my dreams?

Post by jerrytheplater »

Steve, go to the end of the thread where 4d3 "corrected" you and read my post to him from back in June. You'll see some quotes from Dyna-Gro regarding their products. They intend the users of their fertilizers to measure out in volume and not to weigh out the fertilizer. The density of the fertilizer does not matter when using it. You are spending a lot of time for nothing.

The liquid fertilizer contains that guaranteed labeled percentage of the nutrient no matter what volume is used. And no matter what that volume weighs. 1 tsp contains x% N, or P2O5 or K2O, and 1 Tbs of the same fertilizer contains the same x% N etc. Just three times as much because 1 Tbs = 3 tsp in US volumes.

I have not looked at your calculations. I will wait till you read this.
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Re: The Cal-Mag of my dreams?

Post by jerrytheplater »

I see a lot of your posts have just been deleted as I was typing up the post above. I guess you must have changed your mind.
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Steve Johnson
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Re: The Cal-Mag of my dreams?

Post by Steve Johnson »

jerrytheplater wrote: Tue Jan 17, 2023 4:07 am I see a lot of your posts have just been deleted as I was typing up the post above. I guess you must have changed your mind.
Not changing my mind, but I still need to ask you another question before I launch what I wanted to post...

I went on the National Library of Medicine's PubChem website and got the molecular weights of K, S, and K2SO4. The precise calculations show that 1 gram of pure K2SO4 contains 44.87% K and 36.81% S. Of course that applies to 0-0-52, but from what I've seen online, 0-0-50 is a lot more common, and I also see 0-0-53 from a few sources. What's the difference in terms of K and S percentages? Reason I ask is that I want to get the dilutions right for 1-gallon stock solutions with 0-0-50 and 0-0-53 -- it'll come in handy if the people I'm trying to help can't get 0-0-52. I'm also trying to come up with the right ppm numbers for K in the stock solution -- important since the amount of stock solution going into a watering solution determines whether we get the N-to-K balance (K 1.5 times higher than N) right or not.

Thanks for being patient -- whatever small amount of scientific aptitude I have left in this aging brain applies to biology and botany. Even when I was in high school many years ago, I could never understand chemistry or physics.
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Re: The Cal-Mag of my dreams?

Post by MikeInOz »

Steve Johnson wrote: Tue Jan 17, 2023 4:31 am
jerrytheplater wrote: Tue Jan 17, 2023 4:07 am I see a lot of your posts have just been deleted as I was typing up the post above. I guess you must have changed your mind.
Not changing my mind, but I still need to ask you another question before I launch what I wanted to post...

I went on the National Library of Medicine's PubChem website and got the molecular weights of K, S, and K2SO4. The precise calculations show that 1 gram of pure K2SO4 contains 44.87% K and 36.81% S. Of course that applies to 0-0-52, but from what I've seen online, 0-0-50 is a lot more common, and I also see 0-0-53 from a few sources. What's the difference in terms of K and S percentages? Reason I ask is that I want to get the dilutions right for 1-gallon stock solutions with 0-0-50 and 0-0-53 -- it'll come in handy if the people I'm trying to help can't get 0-0-52. I'm also trying to come up with the right ppm numbers for K in the stock solution -- important since the amount of stock solution going into a watering solution determines whether we get the N-to-K balance (K 1.5 times higher than N) right or not.

Thanks for being patient -- whatever small amount of scientific aptitude I have left in this aging brain applies to biology and botany. Even when I was in high school many years ago, I could never understand chemistry or physics.
My text book says K2SO4 = K-44.9 ; S-18.4 I don't think it matters too much what you use. K/N ratio of over 1 will be ok 1.2 or 1.5 or 1.7. all good.
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Re: The Cal-Mag of my dreams?

Post by Steve Johnson »

MikeInOz wrote: Tue Jan 17, 2023 5:48 amMy text book says K2SO4 = K-44.9 ; S-18.4 I don't think it matters too much what you use. K/N ratio of over 1 will be ok 1.2 or 1.5 or 1.7. all good.
Mike, what would I do without you? :)

As a microscope field service technician, I've been in the precision measuring business for a very long time. However, cacti aren't precision instruments, so your information shows that we don't need to be all that precise about how we supplement ferts with Potassium sulfate. Although a K/N ratio of 1.5 may be "ideal", it's good to know about the "wiggle room" I see in your numbers. Thanks!
jerrytheplater wrote: Tue Jan 17, 2023 4:05 am Steve, go to the end of the thread where 4d3 "corrected" you and read my post to him from back in June. You'll see some quotes from Dyna-Gro regarding their products. They intend the users of their fertilizers to measure out in volume and not to weigh out the fertilizer. The density of the fertilizer does not matter when using it. You are spending a lot of time for nothing.
"You are spending a lot of time for nothing" -- yeah, I have a bad habit of doing that. And I responded to your last post before I saw the one above it. Going back to what you said to 4d3d3d3 on 6/14/22, I can see that he was giving me bad (albeit well-intentioned) advice about to send me down a rabbit-hole -- this is something I have to remember:
jerrytheplater wrote: Tue Jun 14, 2022 11:08 pm Hi 4d3

In answer to the question "What does the term Parts per Million mean? on the Dyna-Gro website FAQ https://dyna-gro.com/faq/ They answer "It is a measurement of the concentration of elements in the nutrient solution. One ppm is one part by weight of the mineral in one million parts of solution. For example 9% nitrogen in Foliage-Pro is 90,000 ppm.
We'll apply that formula to 1/2 tsp. per gallon of the 7-7-7 -- 70,000 ppm N/1536 = 45.6 ppm. I had a more roundabout way of arriving at the same calculation, but this is way easier. And it's accurate too, so no need to go down any more rabbit-holes here -- Jerry, your calculations for the Potassium sulfate stock solution are spot-on.
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Re: The Cal-Mag of my dreams?

Post by jerrytheplater »

Steve Johnson wrote: Tue Jan 17, 2023 4:31 am I went on the National Library of Medicine's PubChem website and got the molecular weights of K, S, and K2SO4. The precise calculations show that 1 gram of pure K2SO4 contains 44.87% K and 36.81% S. Of course that applies to 0-0-52, but from what I've seen online, 0-0-50 is a lot more common, and I also see 0-0-53 from a few sources. What's the difference in terms of K and S percentages? Reason I ask is that I want to get the dilutions right for 1-gallon stock solutions with 0-0-50 and 0-0-53 -- it'll come in handy if the people I'm trying to help can't get 0-0-52. I'm also trying to come up with the right ppm numbers for K in the stock solution -- important since the amount of stock solution going into a watering solution determines whether we get the N-to-K balance (K 1.5 times higher than N) right or not.
Steve

Regarding your questions about different manufacturers labeling of their particular fertilizer, in this case K2SO4 and 50-53 % K2O.

Fertilizers have different purity levels. When you calculate via molecular weights you are calculating for 100% pure fertilizer. The only place you'd see that is in a science lab where research is being conducted on the effect of trace minerals on plant growth. You can't have impurities in your fertilizer if you are testing for the effect of 1 ppm or ppb on plant growth. Out in the field or greenhouse or home you don't care.

In the spreadsheet I sent you maybe even a year ago (and I forget exactly which one I sent) I'm pretty sure I added in a correction factor to adjust for purity levels. I know I have on the one I use here at home. 1.5-2.0% impurity is common. For Hydroponics you might see better. The worst would be insolubles as they could clog up the emitters or injectors in the application equipment.

Don't worry about the different purity levels in primary fertilizers. It is not important. Look at how even Dyna-Gro rounds their dilution calculations in that post in the "ppm and Dyna-Gro" post.

And one more thing: Somewhere, maybe in the deleted posts, you were mentioning the oxygen in the K2SO4. In that mention you were talking about it as a nutrient according to MikeinOz. I am sure he does not consider that oxygen as a nutrient. He would have been referring to the needed oxygen in roots obtained from the air as water percolates down through the potting mix. That is why a good well draining potting mix is needed. The O in K2SO4, the H and O in KH2PO4, the O in KNO3, etc. are not "fillers" or "impurities". They are part of the compound being used and are not used in calculating the primary or trace nutrients, except for when calculating molecular weights and percentages in the compound.

Impurities are sand grains, insect parts, wood chips.....
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Re: The Cal-Mag of my dreams?

Post by MikeInOz »

jerrytheplater wrote: Tue Jan 17, 2023 2:07 pm

They are part of the compound being used and are not used in calculating the primary or trace nutrients, except for when calculating molecular weights and percentages in the compound.

Yep. The K2SO4 molecule, for example, has 2 atoms of potassium, 1 of sulphur and 4 of Oxygen. But S can only be taken up in the sulphate form so the O will also get taken up but that amount is miniscule compared to what is taken through respiration.

potassium sulphate.JPG
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Re: The Cal-Mag of my dreams?

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Okay, Mike and Jerry have been giving us a lot of valuable information, so many thanks to the both of you. It would be a shame to have it get buried as our fert discussion threads disappear "below the horizon" when new threads pop up on the Cultivation forum over time. With that in mind, I'm working on a sticky that discusses ferts in a comprehensive manner -- mostly for the benefit of new cactus growers, but it could come in handy for growers who aren't so new and find that their cacti aren't doing as well as they used to. Once I put the sticky up, please feel free to send me a PM on anything that needs to be corrected or added, and I'll update it accordingly.
jerrytheplater wrote: Tue Jan 17, 2023 2:07 pmAnd one more thing: Somewhere, maybe in the deleted posts, you were mentioning the oxygen in the K2SO4. In that mention you were talking about it as a nutrient according to MikeinOz. I am sure he does not consider that oxygen as a nutrient. He would have been referring to the needed oxygen in roots obtained from the air as water percolates down through the potting mix. That is why a good well draining potting mix is needed.
Important point, and I was going to say something to that effect in one of my deleted posts. Here's what I wrote for the sticky-in-progress:
  • "The Oxygen in P2O5 and K2O has no nutrient value, so all we're concerned about is getting the right amounts of the elemental P and K available to our cacti and succulents."
Based on what you just said, this might be a little more useful:
  • "While the Oxygen in P2O5 and K2O helps to support the plant's overall heath, it has no nutrient value, so all we're concerned about is getting the right amounts of the elemental P and K available to our cacti and succulents."
Does that sound good, or is there a better way to put it? If what I just said is accurate enough for our purposes, I'll go with that in the sticky.
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Re: The Cal-Mag of my dreams?

Post by jerrytheplater »

Steve Johnson wrote: Tue Jan 17, 2023 11:26 pm
Based on what you just said, this might be a little more useful:
  • "While the Oxygen in P2O5 and K2O helps to support the plant's overall heath, it has no nutrient value, so all we're concerned about is getting the right amounts of the elemental P and K available to our cacti and succulents."
Does that sound good, or is there a better way to put it? If what I just said is accurate enough for our purposes, I'll go with that in the sticky.
Remember that there is no P2O5 or K2O in the fertilizers we buy here in the US. I would not even mention the oxygen contained in phosphates, nitrates, and sulfates. Those are all ions, and the reason the nutrients are soluble. NO3- is nitrate. SO4-- is sulfate. PO4--- is phosphate. The oxygen in those ions is not considered in fertilizer calculations apart from its contribution to the overall weight of the compound. How much effect is has on a plant as it is watered is something I can't speak to with a whole lot of intelligence, so I won't.
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Re: The Cal-Mag of my dreams?

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jerrytheplater wrote: Wed Jan 18, 2023 12:10 amRemember that there is no P2O5 or K2O in the fertilizers we buy here in the US.
Product analysis in the Dyna-Gro 7-7-7 says otherwise:

Dyna-Gro_7-7-7_specs03.jpg
Dyna-Gro_7-7-7_specs03.jpg (36.25 KiB) Viewed 1018 times
General Hydroponics FloraMicro and FloraBloom:

FloraMicro-FloraBloom02.jpg
FloraMicro-FloraBloom02.jpg (90.11 KiB) Viewed 1018 times
From 8/23/20 -- this is Mike referring to the 7-7-7 and how fertilizers are reported in the US:
MikeInOz wrote: Mon Aug 24, 2020 3:11 amThe 7%N in the fert is the percentage of the actual element available to the plant. The 7P and 7K is NOT the percentage of those elements available to the plant. To convert,.....Use 0.44 x the P2O5 listed (7) = 3.08% of the element P available to the plant. And 0.83 x the K20 listed (7) = 5.8% of the element K available to the plant.
Does this apply only to hydroponic ferts? If so, I'll have to be more specific about it in the sticky.
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Re: The Cal-Mag of my dreams?

Post by jerrytheplater »

Steve

To see what any fertilizer is composed of you need to look at the "Derived from" section. This lists the ingredients used to make the fertilizer. I do not know the components of every fertilizer sold in this world, but I doubt you will find any with K2O or P2O5 as a component. Let me know if you find one, I'd be interested to know. I just read a bit on P2O5. It reacts violently with water-not very appropriate as an ingredient wouldn't you say? See https://pubchem.ncbi.nlm.nih.gov/compou ... -Potential Section 8.1.5 Fire Potential, third line.

I do not know when fertilizer labels were standardized in the US. Nor do I know why they were standardized like they are. But there are both Federal and State regulations governing them. Can I point you to them? No. Probably easily found via a Google search.

All fertilizer labels must report Total Nitrogen as an elemental percentage. For Phosphorus, the amount the fertilizer contains as phosphates must be converted on a molar basis to P2O5. I can not think of any other phosphorous compound besides phosphates. So, you calculate your weight of phosphate in the batch of fertilizer. Convert it to the number of moles of phosphate it represents. And then figure out what the weight of P2O5 would be for an equivalent molar mass. One mole of PO4 in grams weighs 94.97 grams. If that is what your bag of fertilizer contains, then you convert it to P2O5 by calculating the percentage by weight of one mole of P2O5 (141.94 grams, because there was one mole of PO4). You divide 141.94 grams by the total weight of the bag of fertilizer being tested. This is what you report on the label as a percentage as P2O5. Clear as mud?

Same for K2O.
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Re: The Cal-Mag of my dreams?

Post by jerrytheplater »

My mistake: While taking my shower I realized I should have said for each mole of PO4 in the fertilizer you convert it into 1/2 mole of P2O5.

The number of P's have to be equal.
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Re: The Cal-Mag of my dreams?

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jerrytheplater wrote: Wed Jan 18, 2023 3:14 am To see what any fertilizer is composed of you need to look at the "Derived from" section. This lists the ingredients used to make the fertilizer. I do not know the components of every fertilizer sold in this world, but I doubt you will find any with K2O or P2O5 as a component. Let me know if you find one, I'd be interested to know. I just read a bit on P2O5. It reacts violently with water-not very appropriate as an ingredient wouldn't you say? See https://pubchem.ncbi.nlm.nih.gov/compou ... -Potential Section 8.1.5 Fire Potential, third line.

I do not know when fertilizer labels were standardized in the US. Nor do I know why they were standardized like they are. But there are both Federal and State regulations governing them. Can I point you to them? No. Probably easily found via a Google search.
I did some research on the Web, and I couldn't find any Federal regulations on how fertilizers are reported, but I could find them on the State level. Although I don't have the time to go through each and every state, a sampling indicated that the regs are probably uniform in all 50. Here's an example from the Clemson University's Cooperative Extension Home & Garden Information Center:

https://hgic.clemson.edu/factsheet/read ... zer-label/

South_Carolina_guaranteed_anaylsis_label.jpeg
South_Carolina_guaranteed_anaylsis_label.jpeg (86.36 KiB) Viewed 1001 times
I realize that I don't know nearly as much about fertilizers as you do, so you gave me some good education there. However, "Derived from" doesn't matter for our purposes in determining NPK ratios -- all we need is the guaranteed analysis of P2O5 and K2O being reported on the fert's label. To repeat what Mike said in 2020 (using Dyna-Gro 7-7-7 as an example):
MikeInOz wrote: Mon Aug 24, 2020 3:11 amThe 7%N in the fert is the percentage of the actual element available to the plant. The 7P and 7K is NOT the percentage of those elements available to the plant. To convert,.....Use 0.44 x the P2O5 listed (7) = 3.08% of the element P available to the plant. And 0.83 x the K20 listed (7) = 5.8% of the element K available to the plant.

Just a general caveat to our members...

If some states don't have guaranteed analysis regs, don't buy their ferts. And if manufacturers don't have a guaranteed analysis on the label and/or their websites, don't buy their ferts either because you won't know what you're getting.
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Re: The Cal-Mag of my dreams?

Post by greenknight »

The soluble N is what's immediately available to plants, but the insoluble N can be rendered available gradually by microbial action. This example is a slow-release fertilizer.
Spence :mrgreen:
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