Planted Tank Guru
Join Date: Jun 2004
Location: Baton Rouge, LA
Just to clear up the confusion, this tank does not have CO2. The air stone is connected to an air pump.
There is CO2 in air, and that may be what Svitlana is referring to. But it's too little to make any difference in an aquarium. It's also possible she confused CO2 (carbon dioxide) with O2 (oxygen).
About that large plant on the left with white-trimmed leaves. If it's real (and not one of the plastic ones), it's not an aquatic plant and will eventually die, regardless of what you do. Some fish stores are bad about misrepresenting plants this way, and some of the others plants you've had might have died for the same reason. Write down plant names at the store, then check them out online before making purchases.
Blue Green Algae (BGA) isn't algae at all, but bacteria that uses light to grow, as if it were a plant or algae. So antibiotics, like the Maracyn (erythromycin) Tetrameck mentioned, will kill it. That's the easiest and most reliable way to get rid of it, though it's not the only way, nor is it the cheapest. Should you try it, remove as much as possible of the BGA before adding the Maracyn. A lot of BGA dying off at once can be toxic. Once eliminated, it normally won't come back unless reintroduced from another aquarium. That can be one of yours (if you have more than one), or even from the fish store. Checking their tanks to see if they have BGA before you buy will help to avoid it in the future.