Cool experiment. I've grown both Blyxa japonica and E. tenellus without CO2 and ferts. the Blyxa was in 5 year old Florabase which was very broken down in an established tank though, while the E. tenellus was grown in inert gravel with a 28 W T5 NO light and EI dosing. The Blyxa is currently still growing, although it's floating now, as my growout BNP's keep uprooting it. 7 W LED light.
Filstar pimp #59 (shhhh on the Eheim)