Ammonium and nitrifying bacteria, CO2 diffusion

Subject: Ammonium and nitrifying bacteria
Someone wrote:

> > A related question: when one has a biofilter in a heavily plan
> > would the bacteria and the plants be in competition?

Then AMC wrote:
>Yes, that's right.
> > If so, who gets what first?
>They both get some. But, the total amount available to the plants
> is reduced because of the competition with the bacteria in the f
> > the water through while the plants stand around waiting. Thus,
> > are more likely to get only nitrates--which we now know they h
> > time making use of.
> Your picture of what is going on is a little off. Think of it l
> this - You are in a closed room with a burning candle. The candl
> using up O2 and therefore you are competing with the candle for 
> Because of the candle, at any point in time, the amount of oxyge
> had available to you was less that there would have been if the 
> not been there, right? 

> Also, the concentration of NH3 or NH4 in your tank is
> theoretically _never_ zero. When we say that the test kit reads 
> really mean that the concentration is *undetectable*. 

True, but that's not exactly the same situation as we have in an 
aquarium.  We definitely have a finite amount of nitrogen 
available. (in whatever form)  It is _absolutely_ possible to have 
a situation where there is little enough nitrogen (in whatever 
form) available that the plants are nitrogen limited.  

IMO, that's why it may make sense to use excess biological 
filtration in a heavily stocked tank, but not in one that is 
heavily planted and lightly stocked.  In this case, commensurately 
large water changes will have to be done frequently to limit the 
build up of nitrate.

  If you _never_ see any measureable nitrate in your tank, odds 
are that the tank is at least slightly nitrogen limited.  OTOH, if 
you see nitrate levels rising, it's a sign that you are letting 
the bacteria do too much of the work, and not the plants.  In this 
case, look for the factor that is limiting plant growth.  Remedy 
that, and unless the tank is over stocked with fish, the plants 
should take care of ammonia(um) as it is produced and nitrates 
will decline.

As an aside, there should _never_ be any measurable ammonia and/or 
nitrite in a properly cycled tank with or without plants.  These 
two forms of nitrogen should be processed out by plants and/or 
bacteria before they reach measureable levels.


Subject: CO2 diffusion

Francis Ngoh wrote:
> Another twist is to pipe the CO2 under a floating glass jar:
> Borrowing Duncan's picture:
>   ____________r-------n_
>  |_====_________________|
>  |~|o~|~~~~~~~~~~~~||~~~|
>  | | o|  .  <>-<   ||   |
>  | |o |   .          .  |
>  | | o| ><>  \       .  |
>  |   O        |/  >-<>  |
>  |************|*********|
>  |______________________|
>  where o
>       o   are the CO2 bubbles coming from an airstone 
> I inverted a glass jar and let it float under a glass pane that 
> placed across the aquarium.  The CO2 bubbles are placed under th
> After a few hours, when it's filled up, I moved the bubbles else
> and replace them back under the glass jar again when the CO2 in 
> jar is almost fully dissolved.
> A further refinement would be to build a narrow, inverted glass 
> the back of the aquarium to collect the CO2 the same way.  Has a
> tried this before?

While pssive diffusion is better than just letting the CO2 bubble 
out of the aquarium, a reaction chamber, where CO2 is actively 
mixed with the water is much more efficient.  This can be done by 
bubbling the water directly into a power or canister filter, but 
that method makes some noise, and it's hard to count bubbles to 
regulate your CO2 flow.  

I use a reaction chamber made of either the fat end of a gravel 
vac, or a small pop bottle with the bottom cut off.  This is 
attached to the outflow of a canister filter.

____________ | Outflow from filter
___       / || \
   \     /  ||  \
    \    |  ||  |
     \   |      | Gravel vac
      |  |  o   | (or bottle with the bottom cut off)
      |  | o   o|
      |  |   o  |
      |  |  o   |
      |  |__|___|
      |     |
      |_____| CO2 line

There is virtually no CO2 lost with this method.  It is all 
completely dissolved as it tumbles around within the chamber.

Karen Randall
Aquatic Gardeners Assoc.
Boston, MA