With that much light I would start dosing according to the Estimative Index method, or some other method so you are to be adding all the nutrients the plants need. Go back to adding the Excel, too. Plants need the carbon.
Dry ferts can be purchased very reasonably from www.aquariumfertilizer.com
and other sites.
You will most likely need:
Macros (fertilizers plants need the most of)
KNO3, a source of nitrogen
KH2PO4, a source of phosphate
K2SO4, a source of potassium. Potassium deficiency is often indicated by holes in the leaves.
If the GH is relatively low in your water (about 3 degrees or less) then I would get
Seachem Equilibrium or Barr's GH Booster. Either of these will raise the level of calcium and magnesium in the tank, and also supply some potassium, iron and manganese.
Micros (fertilizers that plants use less of, but still need to have supplied)
Iron. Get chelated iron.
All the others are in a mix like CSM+B, a blend of all the trace minerals plants use.
Here is a link to some possible ways to dose the fertilizers. Sort of long, but LOTS of information: