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Re: CO2, O2, Nitrosomonas, and Nitrobacter

Naomi Mizumoto at naomizu at pacbell_net wrote:

> Okay, picture this: a tank with power filter, NO plants, but somewhat
> overstocked with fish, and completely cycled. SUDDENLY, you're adding CO2,
> the line going *directly* into the intake of the power filter. Now, would
> this affect the biological filtration to the point where you'd see an
> ammonia spike? Remember - still no plants.

No more than adding CO2 by any other method. Question is, why would anyone
add CO2 with NO PLANTS?!

> The "consumption" of the ammonia is still only the Nitrosomonas and
> Nitrobacter. Since the CO2 is being efficiently diffused into the water by the
> impellor chopping up the bubbles *right before* going through the bio medium
> (not to mention the localized acidity), I see this killing off a good portion
> of the colonies in the filter.

First off, some canister filters like the Magnum have the impeller *after*
the media, and the CO2 diffusion isn't very noisy. Also, unless the flow
rate through your filter is incredibly slow, injecting CO2 into the filter
will not affect the bacteria any more than injecting the same amount of CO2
by another method, at least not at the rates we are injecting it (a couple
of bubbles a second or less).

> I'd also imagine that in time, re-colonization would occur in some
> spot that were chemically "less hostile" to their existence. Or am I wrong
> again, and this would not affect the bacteria in the filter in any way?

Unless you're pumping a lot of CO2, it's not going to be any more "hostile"
in your filter than if you use any other method to diffuse CO2 into your
tank water. The tiny tiny amount of dissolved CO2 will be almost immediately
diluted and sent out to the tank, so the amount of pH change that the
bacteria in the filter media feels will be virtually the same as what it
feels from the water column at large.

> I needed an explanation of why it's something to watch out for in a tank
> that's understocked with plants and overstocked with fish.

The only thing you need to watch is the pH of the tank. As long as you
monitor that, it doesn't matter how many plants you have: you'll be adding
only the CO2 needed. Adding it in a canister filter is virtually the same as
adding it by any other method.

You can prove this mathematically using pH log calculations in relation to
the flow rate of your filter. Calculate how long it takes your filter to
turn it's own volume over, then calculate how much CO2 is added in that
time. Use a log formula to compensate for the pH differential between tank
water and filter water (which is constantly being diluted by tank water),
then plot that over the time period of filter turnover to find the
approximate change the bacteria will actually feel. It hurts my head
thinking about it, but it's gonna be virtually zero.

An easier proof can be had by doing a simple experiment:

Start your CO2 injection into your filter. At ANY TIME, turn off the filter
and the CO2, and *immediately* check the pH in the filter water and in the
tank water. I bet it will virtually be identical (barring the incredibly
clogged filter scenario).

Dan Dixon