Alright, so here is a rather dumb question but I am only asking to make 100% sure that I am making the right decision.
Here it is: Can you over-dose a betta only tank with CO2? I don't think you can since they are labyrinth organ fish and breathe atmospheric oxygen. But, like I said, I really want to know for sure so I don’t decide to add CO2, screw it up, and kill my fish.
Thank you for your input!
-Mary

No, I believe bettas are safe in a CO2 system. The reason some fish develope an air breathing organ is to allow them to survive in a low O2 environment. Corys go to the top every once in awhile and recharge this organ just like Bettas do. Other fish, that aren't air breathers, also go to the surface and gasp for air when O2 conditions aren't very good. With these fish this is a sign of distress.

I think you can,just because they also rely on the dissolved oxygen to a point.However,I dont think it will be fatal as quick as other fishes.If you are dosing CO2 in a closed tank,then the CO2 will seep into the atmospheric area in the tank,and the fish will have more trouble breathing.

My macrostoma tank is sealed as the brats are jumpers,like many other bettas.These guys however,will hunt for holes to jump out of.I keep a glass top on the tank and its almost completly sealed.I dose CO2.I use DIY.Whenever I add a new bottle of mixture,I have to add an airstone to allow more oxygen in the top area,as they do gasp for air easily,from the excess of the CO2 at the beginning of the yeast setup.

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Thanks Majerah for the advice about the air stone when starting a new bottle. I dont plan on dosing much since I only have a 10 gallon but wanted to make sure that it something happens there is less of a chance of fishy death because I am a moron.