Just a word of precaution, in a 4 gallon, I would worry about too much CO2 displacing the oxygen. If you have alot of fish or other live inhabitants, just keep an eye on them the first day to make sure its not too much. With plenty of plants, the plants will change it over, but you never know. I use a homemade CO2 myself, and saw a big difference in a short time! Posts pics if you can, would love to see the progress!