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Re: Confused about biofiltration

I am forwarding this with Micah's permission...

From: "Micah Johnston" <mjohnston93 at cogeco_ca>
To: <rachelsor at hotmail_com>
Subject: Re: Confused about biofiltration
Date: Sun, 21 Apr 2002 13:09:02 -0500


Just a few quick thoughts from me which might help:

Both bacteria (nitrosomonas and nitrobacter) responsible for the nitrogen 
cycle require oxygen and expel carbon dioxide as a part of their biological 
process.  In any tank there is only a finite amount of nutrients and 
substance for these bacteria to grow.  An efficient tank's bacteria column 
will "level-off" at a point where all nutrients have been consumed.  In 
other words, the levels of bacteria will increase until their food sources 
deplete, as with any natural food cycle.  This means that there is a limited 
amount of bacteria a tank can sustain.  With that being said, one could 
argue to have those bacteria located where desired and in this case on 
bioballs.  The reasoning behind doing this in a planted tank is that the 
bacteria, if living ON the plant leaves, will rob the plants of many 
nutrients the plants themselves require. Even ammonia will be "sucked up" by 
the bacteria before the plants would make use of such fertilizer.   However, 
the prime argument people have made for the use of bioballs, or the like, is 
due to the stable environment they provide as opposed to the conditions they 
might find on plant leaves.  This is as a result of photosynthesis.  As you 
may well know, during daytime plants consume carbon dioxide and expel oxygen 
as a result of photosynthesis, and at night time they expel carbon dioxide 
and consume oxygen.  It's this time, at night, when things become unstable.  
By releasing carbon dioxide the plants kill some bacteria on their leaves 
through asphyxiation and further compound this problem by competing with the 
bacteria for oxygen.  By morning, the levels of bacteria have lowered 
substantially and only begin to rebound throughout the day.  It's not 
catastrophic, but the impact of this fluctuation is amplified inversely by 
the size of the tank, that is, the smaller the tank the greater the impact 
of the fluctuation.  Had the bacteria column been located elsewhere in the 
tank (even if only centimeters away from the plant leaves) the fluctuation 
would have been greatly reduced.

Better or worse?



Micah Johnston

-- Original Message --

I have been reading the discussion about bioballs with some interest,
because I think that after 2 years of fishkeeping I understand the whole
subject less than I did when I started. I understand the nitrogen cycle -
NH3->NO2->NO3, right? What I don't understand is why bioballs are useful in
a planted tank. For one thing, doesn't the surface area of all the plants
act as a place for bacteria to grow? There is whole lot of plant-leaf
surface area in the tank. For another thing it seems to me that the plants
would be able to handle - would in fact enjoy - any ammonia spike which
might happen as a result of adding more fish, overfeeding, or killing off
the biofilter using medications. At least that seems to be the case in my
own tank.

So what am I missing? Why use bioballs (or their equivalent) in planted

- -rs

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