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>>While most of the references tend to be on the more emergent growth or
water species, the trend is still very evident witrh respect to NH4+.
I would NOT expect the rates to be much lower for tropical submersed
species if you are adding CO2 at near saturating values, eg 30ppm or so.
Emergent plants are in another niche and have issues with nutrients such as
transpirational pull, higher light values, non CO2 limiting conditions and
the greater need/allocation for support and longer retention times as
source sink for nutrients. I try to stay away from these plant studies if I
can with more focus on tropical/sub tropical shallow water system with a
relatively high % of plant biomass.

This article raises some issues that I have dealt with such as NH4 being
used rapidly by aquatic plants. The same is true for algae, since they are
much smaller, they have much less demand and get more out of the NH4+ vs
NO3 per ion asssimilated. Once the spore has decided to settle and begin
growth after getting a spike of NH4, then it has enough reserves to use NO3
should NH4 run out. Then it hangs on for dear life(Green water, BBA,
Staghorn etc).

I think if there's one nutrient that is competed for, NH4+ certainly is it
in our tanks.
The trouble with NH4 is the rapid usage by plants, algae and bacteria. It's
gone by the time you add it and try and test.
My NH4 dosing experiments never found any after 2 hours.
One study dealt with bacterial interactions, so they sterilized the plants
prior, there was no bacterial oxidation. I've said that the denitrification
does not cause that large of an effect on aquatic plant tanks based on
removal of the plants then measurement of NO3 levels. That is just a quick
and dirty way to see and not with out issues, but it does seem to suggest a
smaller role, perhaps insignificant. I think there's bound to be some
variation depending on the tank, but overall I think it plays a smaller
role than some have suggested.

The other issue the article raises is how much NO3 plants consume through
The table suggest a rate of close to 3-4ppm per day, pretty much what I've
found in my tanks at full CO2 saturation/good nutrients etc...
It seems less likely that the losses are due significantly to
denitrification and rather more through plant uptake.

But if you take this notion of NH4 is "better" energetically for the plant,
the dosing of this is extremely difficult for the aquarist as a sole or as
a dominate source of Nitrogen, except.............in lower light or non CO2
tanks, then this cation can play a dominating, if not the dominating role.
These tanks get most of their input of nutrient via fish food/waste, wereas
a higher light CO2 tank needs more of it's relative nitrogen in the form of
But this is more practical for the non CO2 method and therefore more
relevant in terms of a source of nitrogen.
I do not add KNO3 to a non CO2 plant tank, growth is slow and it's not
needed. Fish loads are enough to supply the needed nutrients.

But you need some extra CO2, extra light and a little bit too much NH4 to
get the algae.
Generally those are in very short supply in a non CO2 method and these are
some of the main limiting factors for algae in those tanks.

Plants and algae can adapt well to low CO2, but to get the maximum
efficiency from the available light they need the extra CO2, this means
more trouble per atom of Carbon fixed for the algae vs the plants.

Limiting CO2 also limits algae, ALL plants and algae still convert HCO3 to
CO2 or take CO2 in directly.
This in turn limits most all nurtrient uptake.

If a CO2 enriched tank is NO3 limited and it's unlikely it's having it's
NH4 needs being met due to the demand from high light/CO2, then the plant
does not have enough nitrogen to make the Nitrate Reductase enzymne it
needs to remove the NO3 from the water in the first place and this is what
happens when plants "stunt".
They can get back again and it may take awhile, but I've seen this occur
many times and it appears independent of NH4 in high light/CO2 tanks.

As less light/CO2 is added, then the role of NH4 increases.

One interesting point, is the notion of NH4 is taken up by the plant leaves
preferencially over the roots.
This goes back to one of those suggestions many over look. Add as many
plants as you can from the start. This removes all the NH4 so that the
algae don't get any no matter if you add CO2 or not.

NO2 is not used by plants for a simple reason, internally in the cell, NO2
is very toxic to plants. Plants have an excess of NO2=>NH4 for this reason
so that the cell never acculmulates any NO2 as the enzymatic chain converts
the NO3=>NO2=>NH4. NO3=>NO2 is slow, NO2 =>NH4=> glutamine is rapid in
terms of enzyme velocity.

Filterless tanks are good in some respects, but some conversion of NH4=>NO3
is a good thing have should the plants slow down or stop removing as much
Bacteria are better than algae.

I think NH4 is also difficult to dose and is so touchy in large due to
plant biomass. How much plant biomass do you have? This varies a lot from
tank to tank, but many have seen what happens when the remove a
considerable amount of biomass. If you remove a large sword plant, prune a
lot but keep adding the same amount of nutrients etc, then you get/can get

This is the playing around and tweaking part of aquarium keeping. Depending
on the relative consistency of plant biomass pruning, this can change the
uptake. If you are consistent and moderate with pruning, then you typically
will have better luck.
The other big variable for many is the fish load which plays a larger role
in a non CO2 tank than in a CO2 enriched higher light tank with NO3 added

Good stuff.

Tom Barr <<

Diana just informed me there are mistakes in the article she wants to fix
before it goes public...being the perfectionist that she is... so I guess I
was pre mature in putting it up...look for the "revised" version in a few

Robert Paul Hudson

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