All Things Gardening forum: Bring me the chemists! fertilizer math from % NPK to NPK codes to PPM?

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Name: Paula
NYC suburbs (Zone 6b)
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Turbosaurus
May 28, 2018 6:45 PM CST
I'm used to fertilizing my planted tanks on a PPM goal...
I dosed every macro element (N,P, K, Ca, Mg) individually, micro blend, and add extra iron and boron to net a desired tank concentration...

so I can do all of that math- I just don't know what concentrations I should be shooting for when I'm watering with a fortified solution.
I'm wondering if anyone has done the math to convert, say miracle grow, from the suggested dilution rate + guaranteed analysis to come up with the PPM or molar concentrations?

And no, its not as simple as it sounds, becasue atomic weight had A LOT to do with it.

I have a friend who works in an electroplating factory, so I can buy pretty much anything by-the-lb at wholesale cost. I'm not gonna pay $6 a lb for miracle grow when Jerry will sell (give me) potassium nitrate & sodium phosphate for $1 lb, and micro mix for $3
The plural of anecdote is not data.
Name: Will Creed
NYC
Profess plant consultant & educator
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WillC
Jun 2, 2018 8:28 AM CST
Have you had a soil analysis done so you know exactly which elements are in short supply? I assume this is for your outdoor plantings.
Will Creed
Horticultural Help, NYC
www.HorticulturalHelp.com
Contact me directly at [email protected]
I now have a book available on indoor plant care
Name: Kristof
New York State, USA (Zone 6a)
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fridayfishfry
Jun 13, 2018 4:18 PM CST
Turbosaurus said:I'm used to fertilizing my planted tanks on a PPM goal...
I dosed every macro element (N,P, K, Ca, Mg) individually, micro blend, and add extra iron and boron to net a desired tank concentration


This is what I use to make different mixes for different plants.. these proportions are for young heirloom tomatoes

Macro / secondary macro:
1 Monopotassium phosphate
1 Potassium nitrate
1 Calcium nitrate
1 Magnesium sulfate (Epsom salts)
1/8 Diammonium phosphate

Micro:
6/100 Iron Chelate (FeDTPA)
2/100 Boric Acid
1/100 Copper Chelate (EDTA)
1/100 Manganese Sulfate
0.75/100 Zinc Chelate (EDTA)


but to answer what I think is your question..
Parts per million = ppm
PPM = mg / liter
400 grams fertilizer in 378 liters (100 gallons) is 1058ppm

To check how it changes you can use a TDS (Total dissolved solids) meter which gives you a ppm estimate.
Name: Kristof
New York State, USA (Zone 6a)
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fridayfishfry
Jun 13, 2018 4:41 PM CST
Turbosaurus said:
I'm wondering if anyone has done the math to convert, say miracle grow, from the suggested dilution rate + guaranteed analysis to come up with the PPM or molar concentrations?

And no, its not as simple as it sounds, becasue atomic weight had A LOT to do with it


First off don't confuse electroplating compounds with the element you need. Potassium nitrate is OK but I've never heard of sodium phosphate being used as fertilizer.

NPK is already given by % elemental weight of the compound



Los Angeles, CA
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WeGrowCoolPlants
Jun 16, 2018 7:53 AM CST
Learn about the 6 macros and micro nutrients needed for maximum plant health and productivity. Live youtube event this morning at IV Organics YouTube channel

Thumb of 2018-06-16/WeGrowCoolPlants/123d45

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