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Re: NO3/NH4 and eating by filters

>> might "overprocess" the nitrite into nitrates (that the plants
>> should be consuming instead)..
> 
> I'd love to see some more in-depth discussion about this.  I tend
> to run high nitrates, and I suppose there could be something going
> on here related to the wet/dry.   But several things don't make
> sense:  
> 
> 1) Why wouldn't plants be able to use the nitrate?


They do and can. It is the largest portion of N that is taken in by plants.
The optimum *****ratio******* of NH4 to NO3 is 1:4 from most average figures
of preferred nitrogen species from mainly ag crops but also a few other
plants that have been studied extensively. One thing to note here is that
many plants have _different_ ratios of preference. You can argue that
aquarium plant vary largely in this regard.

Plants do not exclusively prefer only NH4 or only NO3.

 For practical purposes though, most plant tanks are NH4 poor or (we don't
truly know) the NH4 is taken in so fast we are not sure what ratio they are
really getting to fill their growth and maintenace requirements since uptake
is likely very fast. Furthermore, the NH4 is at very low levels from
fish/critter waste and  doesn't have any time to build up a residual to be
tested. Plants will take the NH4 up continuosly.
NO3 is a slower process since there are two extra steps involved before
assimilation into NH4. Whether it is the preference for this
balance/ratio(of cation/anion) or whether is due to the 2 steps is not clear
to me at this point.

Some Crypts prefer more of the NH4 than the NO3. Some/most fast growers
perhaps are more interested in whatever they are served. NO3 is generally a
water column nutrient and the NH4 is from consumer (snails, fish,zooplankton
etc) waste, spring turnover events and terrestrial run off. It's perhaps a
good metal picture to think of NH4 in the gravel deep and the NO3 in the
water column. 
Plants do not come from stable benign environments and are good at using
both types of N. That have to make do with what they have. Most aquatic
plants are generalist and are not picky about what forms of N they get.

I can add 5-10ppm of NO3 and it will not induce algae. If I try say the same
1:4 ratio of NH4 thing will not be the same.............
KNO3 is a much better source than ammonium sulfate therefore for our
purposes. Small little pulses of NH4 may help a tank if it's doing well and
thriving. But someone will over do it. They always do. Or think their tank
will do much better by adding it. Just get more fish/critters is my
advice(algae eaters hopefully). That's the best low level continuos doser I
know of. PO4 is different and adding enough from fish waste alone is a
losing battle. NH4 on the other hand is well suited to be introduced via
waste of fish/critters. This makes up the lion's share of the waste
produced. 

If you have a large filter, higher fish load you may not need to add NO3 at
all. I think that is often a goal of many aquarist. At least in the past it
use to be. I have flipped back and forth on the KNO3 issue. Plants do seem
to grow a tad better with some NH4 source.

Whether bacteria contribute any substantial "competition" effect on the
plants or not for NH4 remains to be seen. There are many variables to
contend with when saying "this" or "that" doesn't occur in a plant tank.
Substrates alone constitute large massive bacterial cultures. If that
argument is true why have deep substrates? Likely back to that same idea
that the NH4 is in the substrate and the NO3 is in the water column. But
there is still a large amount of bacteria in the substrate.

 You have some bacteria already there. Why not have a little more just in
case you decide to uproot and move your plants around? That would disturb
the gravel bacteria quite a bit and perhaps even crash the tank, pluming up
some of that NH4 that's been building up deep in the gravel.

Most plants are amphibious. They cannot get any NO3 when above water so they
have to get all the N from the soil. I suspect most of this is NH4 when this
happens.
Take that idea a tad further and use the sub for NH4 and the leaves for NO3
uptake.

 Stable isotopes would be one of the best ways to test to see how much the
each group gets; bacteria , plants and algae.
Folks argue about the filter eating the NH4 and I say it means little in the
scope of it all. Certainly not enough to concern one self about too much.

If you have a higher fish load, bigger than a 55 gallon, I'd go with a
wet/dry. They produce very stable long term plant tanks.

I'd rather undershoot NH4 and NO3 and top off with Miracle Grow(etc), KNO3
etc. With a high fish load the amount of NH4 that has to pass by the plants
is rather high. Seems like the plants get their fill.

>  I know 
> that it takes a little more energy for plants to use nitrate instead
> of ammonia, but is it enough to really make a difference?

I think so. But it's a fine line/slight effect and would be much like are
cable heaters really needed. I draw this idea from a number of no-fish plant
tanks that I've had over the years. I played around with ammonium sulfate
not too long ago and removed all of the fish just in case. Some plants
respond well to slight, and I mean slight, amounts of NH4+. This seems to be
the case with fish waste. Adding fish is far safer and added small continuos
amounts of NH4 into the system. Ammonia is not a practical fertilizer to add
from inorganic sources except in very reduced amounts in pulses. The fish
effect would give better results. Shrimp, snails etc also give off usable
NH4. Plants give off Nitrogen also but it's organic and needs to be broken
down by microbes. That's a good reason to have a big filter perhaps but this
likely has little effects on our tanks.
 
>  As for
> processing nitrite into nitrate, I thought I read recently (from Tom
> Barr?? maybe?) that plants don't use nitrite.

That what I've read in the literature I have. Considering the processes,
physiology, and practical experimentation it make complete sense.
NO2 is highly toxic. Plants covert this quickly to NH4 once they transport
the NO3 to the chloroplast surface. NO3->NO2 is a slower (rate limiting)
process in N assimilation. It's fine to have excess NO3 and have that back
up a little in the cell. You do not want a back up of NO2 though.
  
> 2) I don't have the traditional "wet/dry action" taking place
> in my sump.  I lowered the bio-ball compartment so that the bio-balls
> are always fully submerged in the water.  I still have the
> drip-tray creating the trickle action.

I think it's mainly a function of surface area. Recall that planted tanks
have higher than normal O2 levels. Forget about CO2 for a moment. As O2
saturation goes beyond 100% it off gasses and and we lose O2 just like CO2.
Bacteria use O2 for many processes in our tanks. Plant roots bring O2 to the
bacteria around the roots(involving the substrate). All the surfaces in our
tanks are also rich in bacteria, filter included. But having large filters,
high surface area substrates, seems to help the tanks I've dealt with.
Bacteria friend or foe? I'd have to say friend. Algae are the problem, not
bacteria. Bacteria's uptake of nutrients can simply be added to the tank to
make the difference.

This is kind of like "adding another plant" type of argument. Are adding
more plants not a good idea due to competition? More bacteria or more
plants? ARen't more growing thriving plants better for a tank? The bacteria
only convert NH4 into NO3 though. Plants will go after both.
This all gets back to balance. If you have a load of light, CO2 etc your
going to have to add some traces K+ for decent growth. Same can be
> 
> Personally, I think my high nitrates are just because I feed my rainbows
> a lot, and they can be pigs when they get large.

NH4->NO2->NO3 fast with a wet/dry filter. They are NO3 machines pretty much.
Plants remove it like machines also.
Regards, 
Tom Barr