Flourite is fine, it's my own favorite substrate, and whether or not you need to supplement nutrients more than that depends on your lighting. Light is THE critical factor in driving plant growth.
So before we go any further- what kind of lights does this tank have?
(PS- rinse the Flourite really really REALLY well before you put it in the tank! I take mine outside in a big bucket and rinse it really well with the garden hose until the water runs off clear)