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Re: Biological Filter in planted tanks


On Fri, 14 Apr 2000, Jared Weinberger wrote:

> Adrian Banica wrote "It is still my opinion that plants and nitrifying
> bacteria WILL 'compete' for the available ammonia...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)."

I probably should have written this part of this note in response to
Adrian's letter, but this works.

My understanding is that in nature the nitrifying bacteria are generally
soil bacteria and that they're fairly rare in aqueous environments.  They
thrive in fish tanks because of the high ammonia supply, lack of
significant competition and the fact that we give them a convenient home
to live in (the filter).  Without a filter to live in, with the
competition from plants and with moderate fish loads, nitrifying bacteria
may not be very competitive.  That's not to say that they would be absent,
only that they wouldn't be all that important.

Of course, in a planted tank where a bacterial filter has been recently
removed there may be a large population that continues to thrive for some
time.  In a planted tank that is never equipped with a bacterial filter
there may never be very many nitrifiers.

Jared went on to say:

> We have a heavily planted, heavily stocked 135-gal with commercial CO2. The
> many species of plants are thriving and growth is about as rapid as we
> would like it for most species. We have an Eheim 2228 which is clearly
> larger than "necessary" (when planning our setup we didn't know that the
> plant would be a success and had in mind a full fish bioload). Our nitrate
> is practically stable at about 10-15 ppm and I add potassium nitrate once
> in a while if it drops too low. In other words there is no nitrate buildup,
> although we still do regular water changes. I assume this is a fairly
> common situation in our planted tanks.

I think it was Alysoun who pointed out that some tanks have fish loads
that are too high to function safely without a biological filter.  In
earlier rounds of discussion on this topic someone (and it may have been
Karen R.) pointed out that if your plant growth is sufficient to keep
nitrate levels under control, or if you need to add nitrate to keep the
plants fertilized then you probably can safely remove a bacterial filter.
The plants have already demonstrated that their nitrogen demand is
sufficient to handle the load.

It looks like Jared's tank might be a candidate for less filtration.

> Many species are capable of converting nitrite and nitrate back to
> ammonium, albeit at a slight energy expense. I assume that little or no
> nitrate is being converted to nitrogen and oxygen. So what is the effect
> of this "competition" between bacteria and plants? We feed our fish
> generously and it appears our plants are getting fed as well. I think
> you forgot this back conversion.

I don't know of any higher plants that can't convert nitrate back to
ammonia and I know that virtually all algae can - Euglena cannot.  Ammonia
is the only form that plants can use internally.  That doesn't mean that
they do it without significant cost. I think that the energy they use to
reduce the nitrate back to ammonia is a noticable part of their total
energy budget. If they can get their nitrogen as ammonia instead of
nitrate then that gives them a big energy dividend that they can put to
other uses, like scrounging for iron or just growing faster.  The end
product from removing bacterial filtration should be healthier plants,
less noise from the machinery and less work for the aquarist.


Roger Miller