Let's be careful what we offer for advice to this guy. I'm not sure if you noticed in the first post he stated he's using a 3.7 gallon aquarium. A 3 Liter DIY CO2 bottle will probably blow this aquarium out of the water (figuratively speaking). The most I'd suggest him do to this tank is to buy a Hagen DIY CO2 Kit and possibly try adding a half dose of the packages. These are pretty good for 10 gallon tanks, and you need 2 or more for a 20 gallon, IMO. Although, for such a small tank, it would be best to use pressurized and maintain a small amount of CO2 diffusion safely. Definately more substrate would be a big help. 3" to 4" is my suggestion. Fertilizers are a definate must-have, and they would last for ages on such a small tank. The most difficult part would be measuring out such small quantities of ferts.