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Re: [APD] Macro nutrient ratio
>Is that ratio expressed a N:P:K, or NO3:PO4:K?
A ratio such as the average 7:1:8 for macrophytes is always in
all literature expressed as NPK, sometimes they will use CNP,
Carbon being the main macronutrient
So folks need to divide their NO3 by 4.43 and the PO4 by 3.07 to
get the elemental ratios.
Given that, a ratio of 7:1:8 would correspond to 31ppm NO3: 3.07
ppm of PO4: 8ppm of K+.
Or 1/2 this would be 15.5: 1.5: 4
Anything in this range is pretty much what would maximize the
nutrients you have, but they are cheap and needed in excess at
our scale. So the ratio is of little strict practical importance
but a general guideline nonetheless.
This is why I have maintained that we get all the K+ we need
from KNO3(Steve Dixon asked this question a long time ago).
Unless you have 75% or more of the N coming from fish waste and
tap water, it's very unlikely you will ever have a K+ shortage.
Even well stocked discus tanks seldom can supply more than 50%
of the N from waste in a 2/gal CO2 enriched tank with a wet dry.
>From the ratio at 20:2:5, you can see that you'd need 4X as much
N as K+ before there would the potential for limitation.
Extra K+ will help the plant respond well to stress and other
mineral changes. I know of no known upper ranges for K or P for
Some speculated high K+ causes Ca blockage but this was
speculation only, and poor speculation at that(misapplied
scientific references). A simple test adding high K+ to the
plants in question proved that it could not possibly be K+
causing their issue. Other folks reported very high levels of K+
with the same plant with a variety of Ca/K+ ratios(one of them
won the overall AGA contest with over 100ppm K+ with said plant
as a main group). The folks had issues, I am not going to say
what, but it could not be directly from K+ levels. That I do
know and have proven as well as have over 10 years dosing K+ at
high levels with almost every available plant. No one ever saw
this observation till folks did the bandwagon.
Folks love to speculate in this hobby, but few ever do purpose
driven test, eg no one added PO4 to see if algae really does or
does not cause algae. They were scared and thought it must cause
algae because someone said so in a book.
This is a main factor in the myths built into the hobby.
Reef folks are much more willing to test and look into things
IMO/IME. They also are willing to spend lots of $$$ too!
But.......they are far more reluctant to test and potentially
destroy their reef just to answer a question.
That's why I like aquatic weeds, grow, then kill and then grow.
Marine plants are also good.
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