I used organic potting mix in some of my tanks, topped with sand, as substrate.
Dose with ferts...plants need some trace elements and N,P,K to grow well. As for co2, I inject it into my high light tanks as it allows the plants to grow faster and use up the light and nutrients in such a way as to prevent the growth of algae, as excess light is a great way to get algae growing, trust me.
How long has this tank been set up? You may want to look into pressurized co2 and dosing EI or PPS-Pro....I suggest looking at various plant specific forums on the internet tbh.
You know, saying that, and I've been saying it a lot, I'd love to get some of that info on MFK in a better, less archaic way....I'm far from an expert though but I know where the experts dwell, but there should still be some general guidelines on MFK. If only I had time lol