southpaw wrote in news:nfi6h2d9r6k73saljdpao6l3smgbg1ptgu@
4ax.com:

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?

I imagine your fish will be fine.

Sugar yeast mixes work, but they don't exactly rocket out CO2. If your hood
is ventilated well it should be enough to diffuse CO2 into the ambient
atmosphere. Though CO2 is denser than air so it may not diffuse all that
quickly.

All that said I don't think your sugar yeast reactor will be generating
enough CO2 for what becomes trapped beneath your hood to become a problem.
Since your not using a diffuser most of the CO2 getting into your water
will be due to what is sitting under your hood anyway--trying to avoid any
CO2 surface build-up may scrub your whole effort of using CO2 entirely.
Without a diffuser or a ladder the bubbles just aren't in the water long
enough to make a major impact in and of themselves.

Keep in mind that while Bettas may be able to obtain oxygen from the air
they will rely on their gills when adequate dissolved oxygen is available
in the water. So if the CO2 levels become a problem you will be able to
measure it in your water via your pH shift after the reactor mix starts
working.

Your first indication of a problem may be your Corydoras skimming the
surface--though not as efficient as the labyrinth equipped Betta they too
can get oxygen from the air using their swim bladder.