what percent water change? Flourish doesn't really count as ferts, despite it's label and marketing.
For an LED light, Beamswork DA Fspec seems to be a favorite amongst many on the forum as well as in my local community. Has good par value for the money, and grows plants. The 75 gallon tanks generally are fairly deep too so decent light tends to be more important to have. I'd do two Beamswork for your tank. It's not heavily planted so one strip in the center could do just fine too.
For ferts, you probably need to dose just a little to make sure the tank has all the Macros and Micros. The plants aren't very demanding and you have little so, not like you need to dose that heavily. I would recommend and all-in-one fert for you to make it simple and it should help the plants. Even with dirt/aquasoil, you still want to fert a bit, though you could certainly get away with not in some cases. I'd tackle the lighting first and see if it doesn't improve in 2+ weeks.