One thing the most experienced aquatic plant growers always tell us is to use the plants as the test kit. Do what the plants tell us. You have a lot of light, at least as much as you need, so if the plants don't grow well they are telling you they are short of nutrients. Since the main nutrients are carbon, nitrogen, phosphorous and potassium, it just follows that one or more is in short supply. If you are using the drop checker, with 4 dKH distilled or DI water in it, and it is green, you have plenty of Carbon, assuming you have adequate water circulation to have reasonably uniform distribution of CO2 around the tank. So, that leaves just the NO3 and PO4 to be deficient. (If you have enough KNO3 you will have enough K). Trace elements could be deficient too, but I don't know how to dose that as a liquid, since I only use CSM+B as a powder. Given that doubling the dosage of macronutrients does no harm, I can see nothing to keep you from trying that. If, after a couple of weeks, nothing changes, then you could double the trace element dosing. (Or, double everything at once.) I am almost certain your Excel dosing is not the problem. At worst it would cause trouble with vals or anacharis, and a very few other plants.