I grow lots of java fern, hygro, baby tear, certain blyxa, anubias, variety of floating plants, and certain mosses with about 1.5 watts per gallon. Growth is slower, but hey, I don't want to have my hands in the tank all the time!
I do use pressurized CO2, gasp!, which seems to help even in low light tanks. The only liquid fertilizer that I use is K. I don't have tons of experience with plants, but my limited knowledge has led me to believe that low light tanks need extra K. Someone please tell me if I'm off my rocker. I also dose (sparingly) Flourish-micros.
This set up grows a fair amount of GSA, but only GSA, which I'm happy with. I'm convinced the GSA has provided food for my dwarf cichlid fry, and keeps my SAE and otos happy.
One good gage for good plant growth, and algae, despite your other factors is measuring the Nitrate/Phosphate ratio (http://www.xs4all.nl/~buddendo/aquar...field_eng.htm)
I might be talkin' out my bum here, but I've noticed when I use higher light this ratio is much harder to keep in balance, and is when you need to start adding different nutrients, and more of them.
OK I will continue with my day