Flourish Comprehensive is a trace element mix. You can use any other form of aquatic plant fertilizer with it. You can dose the chemicals, KNO3, KH2PO4, and maybe K2SO4 to provide the nitrogen, potassium and phosphorous that all plants need. Or, you can dose one of the liquid fertilizers, like Seachem Nitrogen, plus Seachem Potassium, plus Seachem Phosphorous. There are a couple of sponsors here who also sell good liquid fertilizers.
Thanks. I'd probably like to try to stay away from the liquid ferts as they seem to be more expensive than the dry ferts. Except for the Flourish of course.