Low light. About 1.75/Gallon.
Plants are micro sword, DHG, Giant Leaf Hygro. Cardinal. Rotala. Narrow Lead Chain Sword. Annubias Nana.
I'm not dosing at the moment.
Considering doubling the light to 3.5 (another identical fixture).
That said, the only plant that isn't thriving is the DHG, and now that i mowed it all down to the nubs, it seems to be coming back some.
Color is decent on everything, but not amazing. I would be using CO2 mostly in hopes that it would make everything a bit more "lush", rather than increasing growth.
Substrate is fluval stratum over vermicompost, which is super rich.
So given all this, think DIY CO2 is worth it?
Your plants will let you know if they need more nutrients.
How high is your lighting? That usually the driving factor in any tank. If you have high lighting you will probably need to dose nutrients no matter what, and you should consider getting more CO2 (or lowering your light level).
If you have low light and a pretty heavy fish load, you can wait and see what your plants do. If they are growing fine for a while and then stop growing as much, that would be a signal that they've used up all the nutrients available to them. It will depend on your plants and your lighting.
Personally I dose the water even in my low-light tanks, because I find it helps growth and fights algae. And if you're already doing DIY CO2, dry dosing is much easier than that.