Yes, some plants NEED the addition of Co2 to even live. These are usually carpet plants. Otherwise "low-light" plants just grow slower without additional co2.
I disagree. I don't love this scape but here is an old tank of mine. 10 gallon, seriously underfilter, no real ferts, no excel on a regular, no co2 at all.
This is where I started:
This is where I ended:
Quote from myself in my thread:
"This has been the easiest tank I have ever dealt with"