Re: Biofiltration/plant/bacteria and Ammonia

[David Aiken <daiken at iprimus_com.au>]

On Monday, July 15, 2002, at 05:48 PM, James Folsom 
<hymy at arches_uga.edu> wrote:

>> 1) The concept of plants "getting to NH4 before nitrifying bacteria" 
>> is a
>> little bogus, IMHO. Plants don't chase after NH4 any more than 
>> bacteria do.
>> NH4 from fish and decomposition diffuses into the water and is 
>> available to
>> all takers equally. Water movement helps distribute it. A molecule of 
>> NH4
>> will be consumed by whatever consumer it comes in conact with. I would
>> venture a guess that bacteria, in general, have a better chance of 
>> consuming
>> NH4 than plants because there are more bacteria and they are 
>> everywhere.
>>
>
> I would like to add something to this:
>
> 1) I would guess that the uptake of ammonia is concentration dependant.
>  Plants having a different optimal concentration than bacteria.  Ammonia
> is present at almost undetectable levels (if not zero) in aquariums.
>  This leads to the assumption that any that is produced is utilized by
> something almost immediatly.  Thus which ever organism in the tank has a
> higher affinity for ammonia at near zero concentrations will consume all
> or most of it.  I would guess that plants  only utilize ammonia when
> there is an ammonia spike.   The bacteria probably get it it the rest of
> the time.
>
> 2) A further wrinkle in this is the fact that ammonia that is not
> produced by fish urinary excretions is produced within biofilms that are
> attached to surface/water interfaces.  These biofilms are complex
> communities, each member contributing something to the others.  Ammonia
> produced from solid waste is in close proximity to other bacteria which
> use it to produce nitrite, and other members of the community use the
> nitrite to produce the nitrate that is released into the water column.
>  Its like an assembly line in a way.  This is why cylcling takes so long
> in a non-planted tanks, it takes time for the community to form.   This
> also relates to why those bacteria supplements don't work so good.  If
> if you add a bunch of all  the bacteria types only the ammonia producers
> and the ammonia users will thrive at first.  The remainders will suffer
> until there is enough of a colony producing nitrite.  If you add gravel,
> mulm or colonized filter media from an established tank, then you are
> adding functional communities of bacteria, and good results follow.
>
> In conlusion ammonia from decomposition is unlikely to be readily
> available in the tank because of bacterial community action.
>

I've been lurking for a few years since I last posted with any 
regularity but this caught my eye, especially since I ran my tank 
without a filter for many years and moved back to using a filter again 
around 2 years ago. I got seduced by the Eheim professional series and 
gave in, although things were working fine without a biological filter.

The comments about biofilm production of ammonium ring true but really 
miss the point a little, I think. Given that there is some ammonium 
going into the water column from fish waste, the question is what gets 
that first and it's there I disagree with James. A healthy biological 
filter will certainly grab some but the ammonium isn't magically 
transported straight to the filter - the water circulates around the 
tank and at any moment some, but not most, is going into the filter. 
Plants have access to any ammonium in water circulating in contact with 
them and they have a pretty fair surface area widely distributed around 
the tank. Much of the ammonium produced by fish is actually produced 
while the fish are in close proximity to the plants, especially in 
heavily planted tanks. I think the plants do the major job and the 
filter tends to mop up a bit behind the plants. Ammonium will be 
exhausted more quickly with a biological filter present, but I don't 
think the difference in exhaustion times is going to be significant in a 
strongly planted tank. I sure haven't noticed significant difference in 
plant growth with or without a biological filter, and i've come to the 
conclusion that my view of some years ago that the filter is 'stealing' 
ammonium from the plants was wrong or, at the very least, an extremely 
exaggerated view.

On the other hand, there are times when I hanker to go back to the 
simplicity of a filterless tank and it's conceptual elegance - usually 
when I have to clean the filter and come in contact with the yucky 
biofilms on the sponges. Still, I stock the tank a bit more heavily with 
fish these days and prefer the possible illusion of a greater safety 
margin given by the filter even though I remain convinced that the 
plants can happily accommodate a larger fish load than many people 
believe.

David Aiken


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