You might not need CO2. CO2 is only necessary if your putting over 2wpg (and its debatable up the 3). At 2wpg, your still going to be able to grow swords, val, java fern, anubias, and the "easier" plants.
If you still want to go the co2 route, you can always just put a diffuser into the tank, I use a wooden air stone that gives me smaller micro-bubbles that have a better chance at dissolving, but there are better options than this.
If you still want to go the co2 route, you can always just put a diffuser into the tank, I use a wooden air stone that gives me smaller micro-bubbles that have a better chance at dissolving, but there are better options than this.