Macro uptake rate ratios - The Planted Tank Forum
Old 03-02-2018, 07:30 PM Thread Starter
Planted Tank Obsessed

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Posts: 373
Macro uptake rate ratios

Does anybody have any anecdotal or scientific information on what the ratio of nutrient uptake is for macros? I've started dry fertilizing but I only have kits to measure nitrate levels so I want to make sure I'm dosing the proper ratio of NPKs such that I don't have major imbalances in the future. Like for every 1 ppm of nitrate is taken up, does 1 ppm of phosphate also get taken up or is the ratio skewed in one way or another?
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Old 03-02-2018, 09:32 PM
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Many rate this @ 10:1 NO3:PO4

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Old 03-02-2018, 09:41 PM Thread Starter
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Quote:
Originally Posted by Maryland Guppy View Post
Many rate this @ 10:1 NO3:PO4
Cool thanks, I'll add that to my excel sheet calculator.
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Old 03-03-2018, 06:29 AM
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Quote:
Many rate this @ 10:1 NO3:PO4
What many people use may not be what plants use.

Note this site list the levels of N and P and many other nutrients. 10:1 N:P does not equal 10:1 NO3:PO4. You can use a fertilizer calculator to convert NO3 to N. I use this one:
https://rotalabutterfly.com/nutrient-calculator.php

Using the calculator
10ppm of KNO3 dosing results in 2.26ppm N and 6.31ppm K
1ppm of KH2PO4dosing results in 0.33ppm P and O.82ppm K
This results in a total of 2.26 N, 0.33 P, and 1.13K

When scientist measured the amount of each nutrient inside plants they found this
http://soils.wisc.edu/facstaff/barak...6/macronut.htm

If we use this scientific data to calculate a ratio we get:
Plant nutrient ratios:
Macros
N=1
K =N*0.666
Ca=N*0.333
Mg=N*0.1333
P=N*0.1333
S=N*0.0666
CL=N*0.00666

If we assume this s the actual nutrient ratio plants need I can calculate the P and K values for 2.26 N which works out to:
2.26ppm N, 1.505ppm K, and 0.301ppm P

For the 10:1 NO3:PO4 ratio we calculated earlier:
2.26ppm N, 1.13ppm K, 0.33ppm P

The two are different. K and P are higher than the science suggest. Is that a significant difference? It looks close but I am not a plant so I don't know. We also don't know how much of a ratio variation there is between the different plants that one can buy. Also the NPK ratio might change from day to day due to differences in leaf, flower, and root growth. There is a lot about plants we simply don't know. So if someone tells you this is the exact ratio you need I would not treat it as fact.

Also don't forget about the other macro nutrients Ca and Mg which are found in plants at higher levels then P. or S and CL levels which are found at levels lower than P. If any one of these are deficient your plants will consum NPK at a significantly slow rate and maybe at a very different ratio than listed. Also any deficiencies in the micros will affect N P or K consumption rates.

If your interested I have also calculated the micro ratios based on the science data I referenced earlier: Micros
Fe=1
B=Fe*0.20
Mn=Fe*0.50
Zn=Fe*0.20
Cu=Fe*0.060
Mo=Fe*0.001
Ni=Fe*0.001

Note Fe=Cl

Last edited by Surf; 03-03-2018 at 06:41 AM. Reason: corrected incorrect link
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Old 03-03-2018, 07:04 AM Thread Starter
Planted Tank Obsessed

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I'm glad you did that calculation out. I calculate everything in reference to 5 ppm nitrates in 10 gallons (size of my tank) but all the calculations are quickly converted to molarity so all the calculations end up being easy (KNO3 = 1M K+ plus 1M NO3-). So if I put 1M NO3- in the tank I'll want 0.16M (PO4)3- and I just need to back calculate the mass from that. Makes thing way easier when figuring out dry weight dosage.
I had a banana plant in my tank that pretty much sapped all the nutrients in my tank because it grew so fast so I'm trying to get things back on track. My monte carlo carpet just stopped growing and there was a pretty bad case of green spot algae, but things are starting to bounce back and I'm seeing new growth in all of my plants. Also i was considering getting otos a month ago so I wanted plenty of algae in the tank for them to eat. I've since switched to RODI water with remineralization so my tank has plenty of Ca, Mg, K, and S in it. What's interesting though is that my TDS tends to drift up over time rather than decrease as expected with the new growth.
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Old 03-03-2018, 11:55 AM
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Quote:
Originally Posted by Maryland Guppy View Post
Many rate this @ 10:1 NO3:PO4
May not be what is found inside plants, but I too have found roughly 10:1 N:P seems to be the sweet spot for me. That is in practice not theory.

But who knows, I'm sure others have completely different results. That's why most use trial and error to see what works best in their unique environment.

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Old 03-03-2018, 03:02 PM
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This is all estimative anyway.

You can put all the math and spreadsheets away for just a moment.
I'm not making a new micro batch today.

If 10:1 is maintained in tank (figure out your own dosing) from KNO3 & KH2PO4 your plants are not starving for NPK.

Regarding Ca Mg etc...and any other macros all of our water sources are different.

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Old 03-04-2018, 01:21 AM
Algae Grower

Join Date: Jun 2013
Posts: 78
There two sets of parameters concerning aquarium or any habitat: 1) Environmental Condition; 2) Demand and Consumption

For planted tanks, the sets of parameters may look like this. What are the numbers? (million dollar question)
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Last edited by max88; 03-04-2018 at 01:54 AM. Reason: million dollar question
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