you can have a ton of plants and never need to add co2. It just depends on WHAT plants. I've had planted tanks for years and have never had high light, co2 or ferts. When you start introducing stem plants and red/purple colored plants, you usually need to start adding these things. There are a ton of grasses, crypts, swords, ferns, etc that can grow very happily and lush, without anything special. I would really recomend you start there, to determine if this is even right for you. Just now, after 8 years of having lowtech lushly planted tanks, I'm upgrading to a hitech setup because I want to try different plants. But be patient and start with some undemanding plants.
