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Re: Biowheels-CO2-plants redux
Karen wrote:
> > OTOH, bio-wheels are _strictly_ biological filtration, so they compete
> with
> > the plants for nitrogen. If your tank is over stocked or under planted,
> > they will give you a margin of error. If you are having trouble keeping
> > the nitrate levels up in the tank anyway, biological filtration is more of
> > a nuisance than a help. (If you have to change water to keep your nitrate
> > levels reasonably low, you probably benefit from the bio-wheels, if you
> > have to add nitrogen, remove them)
To which Shannon Wheeler responded:
> >Is the consumption of nitrate by the bacteria really significant? They seem
> >to have left enough for the algae. BTW, can anyone recomment a good,
> >sensitive, accurate nitrate test kit?
I think that Karen has kindly written and repeated this and very similar
advise at least a half-dozen times. This time she may have omitted some
details that caused a little confusion.
Karen refers to two different cases of nitrogen supply in aquariums.
In one (the common) case, the tank isn't planted or maintained to consume
as much nitrogen as is added to the tank in feedings. Nitrate levels
build up and are controlled by water changes. In this case the aquarium
needs biofilters to protect the animals in the tank from ammonia, because
the plants can't do it.
The second case is what we see in heavily planted, well-lit and
well-maintained tanks; the plants consume at least as much nitrogen as is
normally added by feedings. In this case the plants are competing for
nitrogen and some people add additional nitrate to keep the plants
supplied. In this case there is little chance that ammonia will ever get
high enough to stress the animals. Biofiltration in general and
bio-wheels in particular aren't necessary.
Biofiltration and has some undesirable side effects: 1) the bacterial
conversion of ammonia to nitrate produces acids that slowly destroy the
buffer capacity, 2) the nitrate that results from nitrification has to be
converted by the plants back to ammonia and amines before it can be used
and that requires energy from the plants, and 3) the extra turbulance from
the filter - especially from bio-wheels - tends to drive out CO2 that the
plants need.
As a result of the side-effects, if biofilteration isn't needed for the
safety of the animals in the tank, then it shouldn't be used. Take the
filter off. use it in some other tank and save yourself the cost of
buying a new filter.
Then, Matthew R. Sprague wrote:
> Doesn't the first paragraph above contain some inaccuracies?
No.
> Yes bio
> wheels do compete with plants for nitrogen products such as ammonia but not
> nitrates.
Ammonia and nitrate are both nitrogen sources for plants, but they are not
equivalent sources. The bacteria consume the energy content in the
ammonia, producing nitrite and nitrate. The plants have to put energy
back into the nitrate in order to use the nitrogen. As a result there is
competition for the ammonia nitrogen and the presence of biofiltration is
an unnecessary burden on the plants.
> Bio wheels produce nitrates and if one is having trouble keeping
> nitrates up then a bio wheel would be beneficial to the system not a
> nuisance.
This conversion is not beneficial. The biowheels are not *making* new
nitrogen. They are converting ammonia (good for plants) that is already
in the water to nitrate (not as good for plants) without adding anything
new. This is a net detriment to the plants.
> The bacteria that utilize nitrates for energy are found in anoxic
> regions and would not colonize a bio wheel. This makes the staement that a
> bio wheel should be used if water changes are needed to reduce nitrates
> false as well. The exact opposite would hold true.
The need to control nitrate with water changes is an indication of a
nitrogen oversupply in the tank. When nitrogen is oversupplied then the
biofiltration should be used for the safety of the animals. It has
nothing to do with denitrification in the bio-wheel. That was entirely
your inference.
> Yes the consumption of nitrate can be significant if anoxic regions
> exist in the tank. Some bacteria are so efficient they can even reduce
> nitrate all the way to ammonia.
Karen doesn't mention bacterial consumption of nitrate. Regardless of
whether or not it occurs, it isn't relevant to her explanation.
Roger Miller