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NO3 vs NH4

If folks want to, they can search my older post about these two.

Folks often seem to think there's this simple process going on
in plants about these two ions. Well, it's not. I'll lose a few
of you getting into why but I'll touch on some ideas with 1/3
less jargon hopefully. 

Plants are not static, they have the ability to change things
inside and outside their surroundings. They will take what ever
is there should it be low _OR_ become low.

Low concetrations of NH4 can bounce daily, hourly, weekly etc,
they can be enough to supply the plant for awhile then the
supply runs out. Plants have to switch gears(they are pretty
good at this) and go after NO3 when this occurs. 

There are inducible enzymes that will take in the NO3 when the
NH4 level drops, gets too low and a signal is sent to the gene
through several steps that induces the NO3 enzyme back into
action. This way the plant always has a good supply of N and
takes the easy stuff first should it be available. You will grab
the fish that jump into the boat and then go after the one's in
the water later. Same deal here.  

But plants will do just fine with a diet of nothing but NO3 for
many years.

Folks parrot "a plant perfers NH4+ over NO3-" but as far as
growth is concerned, a balanced ratio grows plants the best(A
anion/cation balance provides the best uptake/growth), so say
for corn, it's about 1:4. Folks should also consider besides
either/or, both combined which is _more realistic_ to most
folk's tanks anyway..........I've tried to add only KNO3 for
about a year to one tank. Many folks liked the plant
health/colors from that tank more than others actually(no fish,
only snails and no foods added, just KNO3, K2SO4 etc....)

A non CO2/carbon enriched tank can have all of it's N supplied
via NH4 very likely from fish waste since the N needs remain low
since the plant is limited by the amount of CO2 or light

But a CO2 enriched tank will need much more NH4 than the system
can handle without also giving ALGAE a nice free easy meal and
induce them into blooming all over your tank.

I've shown this to happen in numerous tanks and have repeated
the same findings in controlled tanks.

Keep adding a fish/shrimp etc till you hit a breaking point
where the system starts to become unstable and the algae blooms
begin. That's the max NH4 uptake the tank can handle without
getting algae. 

NH4 is something you need to balance and have very little of in
your tank. You get too much and you'll get all sorts of algae
depending on the lighting level. 

I'm likely one of the few folks that has done heavy NH4 and NO3
doses together and separate. I saw little difference except for
the algae blooming. 

People also squawk or complain about their plants growing too
fast etc. This is not going to make your plants grow much
faster(dosing NH4) anyway. Sticking with NO3 is perfectly fine.

I was very hard pressed to see any plant related differences
separately but combined did seem to produce better growth(which
is what I had predicted and is more realistic to our planted

There is the practical matter of dosing NH4 from salts, I do not
recommend anyone do this for algal reasons. Fish/fish food
should ideally supply this component(NH4).

That's part of the balance.
The rest of the N should be made up by the KNO3 etc. 

Non CO2 tanks are great since they need little except the
feeding of the fish which supplies the NH4/PO4/Fe etc. You don't
have to dose, do water changes, use as much light etc.
Their growth rates are slower and deficiencies take longer/don't
appear at all since the nutrient demand is much smaller.  

I do have issue with FW planted tanks being Fe limited and that
this controls algal densities while allowing plants a good
supply. I've found this to be a tough sale. While in the middle
of the ocean does have some Fe limited regions, a tank with FE
in the soil/substrate and plants with roots, will not be
limited. Algae need very very little Fe, much less than PO4
which is extremely tiny.
Plants also leak a fair amount of nutrients ertc into the water
column. Both diffusion and plant leakage issue would have to be
addressed and well argued against to show this to occur in a
planted tank. Then there's the fish/critters which also
use/possess Fe. I certainly do not trust hobby test kits to
measure iron in the water column, they are bad.

Also, much like NH4, the supply is used as quick as it is
diffused/leaks out/from fish waste etc. This makes tracing how
much/where it goes much more problematic. You can label the N in
the NH4, Fe etc and try and follow it that way but that's not in
the realm of the hobby and more for the science field... but it
can be done and elucidated.  
Tom Barr



Growth rates are important when dealing with uptake/plant

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