Flourite is not a nutrient-rich substrate. You have to add fertilizer.
You shouldn't use CO2 unless you're fertilizing. And you definitely need to raise your light fixture until you are familiar with the amount of PAR it's putting out and have a good handle on how much you need to fertilize.
May be a good idea for you to review the lighting stickies and the fert/water params stickies in those respective forums. They will help you out tremendously.