Re: biofilters and plants etc

[Thomas Barr <tcbiii at earthlink_net>]

> I have to confess that this had never really occurred to me, either.  I knew
> that plants prefer to take up ammonia rather than nitrates, but I guess it
> hadn't really clicked.

Plant PREFER both NO3 and NH4. Not one over the other, all or nothing
etc. Most crop plants prefer a ratio of 4:1 NO3:NH4. An optimum level
of NO3 is about 5-10ppm but if you attempt to mirror that ratio with
NH4.......you get lots of dead fish/lots of algae.

This so called "preference" is not in anyway absolute nor is something
one can generalize across the board for all plants, each plant has
it's own preferences to how much NO3 it like and how much NH4 it
likes. These levels can and do vary widely depending on plant type.

Now what the hell does all this mean? Plants do just find for years
and years with just NO3 as the only source. They grow wonderfully etc.
If one wishes to add some NH4, add some fish so that you get a little
bit. Do not add NH4 etc.

As far as plants preferring NO2 over NO3, some one is "out to lunch".
Plants don't use it. Don't believe it, try it yourself. Watch plants
remove the NO3 and leave the NO2 for weeks(the levels of NO2 sit there
stagnated for well over a week even in a fully planted tank), even if they
are N limited, they will not take it in.
I've done searching for these so called NO2 references but they are vague at
best concerning NO2 uptake. Most references involve the rapid conversion
from NO3 => NO2=> NH4 on the chloroplast wall, not outside in the water.

NO2 is a toxin in the Cytoplasm and the enzymatic process that converts it
from NO3=> NO2 is a slower one that the NO2=> NH4 conversion, this one is
very fast. In this manner, no NO2 ever is "backed up" in the cell.

There is a slight, and I mean slight, preference for NH4 vs NO3 but
in the end you'll gain nothing, nor see any improvement by adding one
vs the other. I've done this on planted tanks. Doesn't help. The
amount of energy gained is so small that one would extremely hard
pressed to show any differences in a planted tank.

If you pick out a specific controlled study, use a single species(this
doesn't represent all species now does it?) and use only NH4 and only
NO3 in a chemostat and measure dry weight masses/N14/N15 ratios,
you'll get a higher uptake of NH4 in Egeria for example. Not many
folks would add 2ppm of NH4 either. Is this practical and what can
applied to a plant tank here? These studies also don't include obvious
issues such as adding CO2, a full 40% of the plants dry
weight.............
Some arguments are made based on saltwater sea grasses. These plants
along with Egeria, use HCO3=> CO2+ OH- instead of
CO2.............

Water Plants in nature, and specifically those that have been
studied(hornwort, Egeria, Vals etc), use HCO3, a negative ion for a carbon
source. All algae use this ion as their carbon source.

 Adding CO2 changes this balance. A positive NH4 ion in a basic environment
is traded for a negative NO3 ion in an acidic environment. This change
things concerning uptake. Uptake of ions is/can be pH related. Plants can/do
actively change the pH outside their roots/leaves in order to obtain
nutrients. Nitrogen is no exception.

Assuming a CO2 enriched tank has the same preferences as a natural pond or a
controlled study sometimes can get you in trouble. Especially when there's
no observation in our tanks that plants "prefer" one the other. I've tried
this myself. I could not see any and I got lots of algae as I attempted to
keep the NH4 up. Obviously, NH4 is not something to add to one's tank. NO3
on the other hand can be used as the only dosing source of N for plants.

 It's not all or nothing and it makes no difference given the volumes of
Nitrogen needed. You could not add that much NH4 without killing your fish.
 
> Now check me on this: removing the biomedia from your filter does not
> necessarily equate to removing all of the beneficial bacteria, correct?

To some degree.

> Sure, the bacteria will colonize biomedia more effectively than they
> colonize every other surface in your tank.  But they're still out there,
> right? 

Some.
 
> After all, we would not want to remove ALL the beneficial bacteria.  A
> relatively small population (when compared to the bacterial load found in
> specially designed biomedia) would serve as a buffer against plant failure.

Yes, would you rather have a back up or algae? I'd take NO3 over NH4 anyday.
  
> They would also - and I'm going out on a speculative limb, here - uptake
> ammonia and nitrite at night, when the plants are "asleep."

No, they'll take it in most of the time. Plants do not take in NO2. Just NH4
and NO3. A few bacteria take in N2 and NO2.Bacterial colonies will take in
the NH4 at night but so do plants.
 
> This assumption - if correct - should provide some reassurance for people
> who want to remove their biomedia.  As long as there is good water movement,
> the bacteria will be doing their part - just not as aggressively as if you
> were pumping the water through biomedia.

I'd keep the biomedia. Every tank I've messed with has done better with,
rather than without, over the long term.

These tanks were tortured well. I played with adding just NO3 and just NH4.
I watched the plants and the algae. Many folks that are running a "lean"
tank will get an "improvement" from this extra NH4. A similar improvement
was noted when I simply added more NO3...........
 
> Of course, the financial aspect is what's really disturbing.  If a planted
> tank truly only requires mechanical filtration, this is a glum conclusion
> for those who have paid a small fortune for imported German canister
> filters. 
> - Erika 

I don't think those nice canister filters are about to go out of style nor
find themselves no longer needed for plant tanks. Or wet/dry trickle
filters.
Bottom, line, don't worry about it, add KNO3 for a source of N to NO3
of 5-10ppm. Add moderate fish loads.

Regards, 
Tom Barr