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Re: Plants & bacteria

>Thanks to all of you who got involved in this topic. It does seem that quite
>a few people are running their tanks with minimal biological filtration
>quite successfully. Some very interesting points were brought up. Tom Barr
>mentioned that he recalls reading (or hearing) that plants use 25% NH4+ and
>75% NO3- to derive their Nitrogen requirements.
>www.hydrofarm.com/content/articles/factors_plant.html also lists this same
>ratio (together with references) but also brings up the subject of ammonium
>toxicity (another topic). Roger Miller brought up the point that nitrogen
>uptake in plants might happen both during the light and dark cycles. 

I agree
>with Alysoun's opinion though, that the plants ability to uptake any N would
>be inherently limited by the availability of other nutrients and hence if we
>have an imbalance, ammonia might indeed shoot up.

This would happen, **if** there's an imbalance, regardless of bacteria or
not. The bacteria will still be present but not as responsive or have the
same capacity ....as say in a filter(plant or bacteria) to the changes.
Plant filters do both though, combining both plant and bacterial filtration.
This goes back to balance not competition. You can limit any system if you
want too and say it's competition. This is true in nature but in our tanks
we can add whatever we wish to help. This same arguement can hold true for
plant vs plants in that case. I think the idea is more what you want for
that ratio of Nitrogen; and what you want to grow really and it's role in
your tank. Heavy fish loads may need more plant  or bacterial filters (plant
filters are both), lighter fish loads/smaller tanks can use submersed plants
only etc.

>And now lets get back to the biological filter. It is still my opinion that
>plants and nitrifying bacteria WILL 'compete' for the available ammonia.

Some folks do not want a plant filter. They will strive for a submersed only
tank with a smaller balanced fish population. Those with more fish can use a
plant filter etc. If there are more plants inside the tank or in the filter
the plants will remove the waste. 
It's just like having more room or a bigger tank with more plants is all.
You just fed more or add more KNO3 or more iron etc. Same goes for the
bacteria. But we get back to this ratio for good growth of the plants. It's
balance, balance, balance ........ we have the control to add what the
plants need. If you want a bunch of fish in there well, then you'll need
more plants to take care of the job or a plant filter etc. Perhaps you like
bacteria for a filter but bacteria just are not as pretty!

14>First, lets look at a simple case study. Assume that we have a bare tank
>fully cycled (this would mean we have some sort of ammonia source like fish
>waste). Fully cycled would actually mean that we have large amounts of
>bacteria capable of reducing all the ammonium to NO2 then to NO3. Both
>bacteria (nitrosomonas and nitrobacter) are lithotropic requiring oxygen and
>their food source (NH4 or NO2) to survive and multiply. If either one of
>these two are limited their colonies will die back to a new point of
>equilibrium. Testing for NH3/NH4 or NO2 in this hypothetical tank will read
>0 ppm. Now what happens if we introduce plants to the tank? The outcome is
>dependant on a number of variables including the ability to get to the
>ammonia first (is it the plants or is it the bacteria?), limiting factors
>(like nutrients for the plants or oxygen for the bacteria. Bacteria will
>also be limited by the available surface area in the tank), water
>circulation (the ammonium ions would have to be in direct contact with the
>aquarium surface for the bacteria to be able to use it, the same would apply
>for the plants), etc. It is feasible to assume that the plants will get to
>some of the ammonia (especially if we do have a slight water current to mix
>things around) which should cause some of the bacteria colonies to die back.
>Eventually a state of equilibrium should be reached which again will be
>dependent on the exact conditions we create. This is also the opinion of
>most of the respondents to my original post (Cathy, Tom, Roger and Alysoun).
>I would go as far as saying that adding media that offers a large area for
>the bacteria to colonize and then running water over it would not be in our
>best interest (if we are trying to grow plants that is). 

One point............ what about the gravel/substrate? Should we not have
this? Is it not a filter/chemical exchanger also? Doesn't it have
bacteria(lots and lots) in it? Should we have only a very small amount of
gravel? I think it gets back to the point of where the bacteria is, not the
idea of competition really. Using a plant filter and /or the substrate with
plants seems the best notions IMO. The balance and the competition is eased
perhaps due to bacteria being on the bottom away from the ammonia(letting
the plants get at it first) and the NO3 being everywhere which should be
more in line with the ratio of of NH4/NO3 of 25/75. A good argument for slow
flows through the substrate,which doesn't jive with my RFUG's notions but
they do better with higher fish populations also so maybe there's more to
this. Maybe not. 

Of course, as
>Alysoun mentions, there will be a point where the bio load is so high that
>neither the plants nor the available colonization surface is enough to
>'filter' out the ammonia and one or the other needs to be increased (Tom is
>suggesting more plants, another option would be filter media).
>There is a second case to consider and that is starting a new tank fully
>planted up before any bacteria take a foothold. Will the same equilibrium
>point be reached as in the first case or will it be different.

 I'll leave
>that for the next post.

Me too.
Tom Barr