Pete wrote:
On Thu, 21 Sep 2006 19:49:19 -0700, southpaw wrote:

Just a quick question.

I've got a planted seven gallon tank, cycled, with a male betta, 2
cherry barbs, and two corydoras trileanatus. I've been toying with the
idea of setting up a basic DIY 2 liter yeast reactor, as my plants
(some anachris, a red tiger lotus, and some didiplus) are doing ok,
but not much more better than that.

I've done my research. I have fairly hard water tap water that tests
out in the 1.2-1.3 range with slightly above neutral Ph, so I'm not
worried about buffer crashes. But since I'm just bubbling the CO2
straight to the surface and not into a diffuser, I'm worried that a
surface buildup might harm my surface breather. The hood on this tank
is vented. Will that be enough to keep CO2 above the water surface
from reaching toxic concentrations?

Thanks for any help.
I have around 10-12 gourami in my tank which has pressurised CO2
bringing the pH down from around 7.7 to 6.2, so there's a lot of CO2
being disolved, and they're showing no signs of distress, and they
still take a gulp of 'air' now and then.
Each of my 2 reactors is disolving around 8 bubbles/sec, a little does
escape, so there's probably a bit of a layer of CO2 above the water.

There's no point in letting the CO2 just bubble to the surface, you're
probably losing about 99% that way - no bubbles should actually reach
the surface, they should disolve before they get to the top.
Use a reactor or diffuser of some kind.

Wild gourami use their labyrinth to store air when the water in their
native environment is so poor that it can't hold oxygen. But their
gills provide sufficient oxygen in normal water.
Some live in little more than large muddy puddles.

Good luck
Pete

Gouramis and bettas don't "store" air in their labyrinth organs. They
use them like we use our lungs.
It's a secondary means of getting oxygen. Mainly, they get it through
the water via their gills. When it's depleated, they get it from the
surface via their labyrinth.
Now, they always must be able to get to the surface, no matter how well
oxygenated the water is, or they will drown!
This is a fact.