idk about lighting being the issue, but probably your problem is that the vals arent the dominant plant in your system yet. something else is growing faster than them, and is slowing the babies down. Also my tank gets dosed. I dose a tiny amount of iron every single day, potassium 2x a week, and flourish 2x a week. I dose according to the online flourish dosing calendar they give you where you can input your tank's gallons and it will give you how much to dose of each product.
I just take what they give me, and i dose less, plus i dont dose everything obviously, just the potassium, and flourish mainly, and a bit of iron. My tap water has most of the iron already, the phosphate and nitrate come from my fish, so i dont dose those. I have to say everything grows great. i no longer dose excel because of pressurized CO2.