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Re: CO2/Wet drys/low O2

> In his mail on "Trickle Filters and CO2", Roger S. Gordon pointed out that the
> best way to ensure high levels of CO2 are "to keep the surface glass smooth",
> thus preventing the CO2 from escaping into the air above the tank

This is not the "best way" good CO2 amounts. Unless you don't like your
fish. Adding more CO2 to compensate for the small losses from a little
surface movement or overflow boxes is far better "method". You need to work
on how to add CO2 better of you have troubles adding enough CO2 or turn your
needle valve up a notch.
> 
> The unfortunate by-product of this is that the surface area of a still surface
> is much lower than that of a highly agitated one, and therefore much less
> oxygen dissolves into the water and this can be harmful to fish.

Well there's just less mixing and less gas flux between this layer when
still. The thin film that hinders the gas diffusion is thicker. It has
little to do with actual surface area unless your talking about the film
being thinner in spots from turbulence and this is what your calling surface
area. Adding small tiny bubbles of gas/air below the surface helps also like
when a filter or an airstone adds bubbles. But your idea is quite correct
about the fish and in concept. Think about the aerobic bacteria/tiny inverts
also. They play a big role as well.
> 
> I know that some hobbyist get around this by using a timed air pump to switch
> on after the lights go out on the tank and the photosynthesis has halted for
> the day, but what I was wondering is, has anyone experimented with direct
> oxygen injection into the water? Probably through a similar rig to a CO2
> pressurized canister kit with a bubble diffuser, and if they have, what
> results they achieved?

Amano used a disc for adding air. Not O2 as I had thought at one point not
long ago:). I might get to it some day but I think the practicality of it
certainly outweighs the usefulness. I tried the air at night thing. I really
did not care for it and there are "better methods" to take care of this
issue.

A "smart chicken" would just increase their surface movement and water flow
and add a bit more CO2 to compensate the small amount of losses incurred.
It's not illegal to have surface movement:)

Folks are way to anal about their surface movement. Give your fish a break.
CO2 is cheap and easy to add.

 CO2 addition is not the most precise thing if you have a non moving
surface. Why is this?
Gas exchange across a surface is lowered if there's no mixing or movement
etc. While you have lots of CO2 building up in the water there's less O2 to
be had coming in from above. The counter to this is that the plants add O2.
This is true but not all day and all night. They add a large amount about
1/3 of your typical 24 hour day. The rest of the time? Not much. This
variation in O2 levels also affects your bacteria which are very important
to your tank. What's all this mean? More variation in your CO2 levels and
more algae and problems with fish gasping. Just to save a little CO2? Uh
huh. 

Another big issue is when there's little to no movement across the surface
you often get a thin film. Sometimes you can see this film. This film will
lower the rate of gas diffusion across the layer. It will help keep CO2 in.
Adding some movement will reduce the film thickness in most cases a fair
amount. A wet/dry filter helps to stabilize O2 levels that in turn help the
bacteria do better. You can do fine without a wet/dry etc but surface
extraction along with the wet/dry portion certainly helps. If you don't have
this, I would highly recommend that you have surface movement. Quit being
anal about losing a small amount of CO2. For more look at Booth's old post
not long ago on this one and his web site. This is old hat therefore check
the archive if your into it.
Regards, 
Tom Barr