Nice looking tank, is that A. Viejita on the right side on D31-what strain is that?
I'm no expert when it comes to ferts, light and CO2, but in my opinion.., Looking at your before and after, I think it's safe to say you don't have enough light for a carpeting plant like that. Also, I would not be fond of the amount of stray light you are getting with your light so high up. I mean how can you enjoy your tank with 4 bulbs of T5 HO blasting you in the eyes!
My suggesting: move it back close enough to the tank where viewing is enjoyable, and get some floaters like frogbit or dwarf water lettuce to shade out some of the light. Also keep the photoperiod to 8 hours or less. In my mind when I think of algae and light, the longer the photoperiod the better the algae will do. I'd rather have high lighting for a short time, than weaker lighting over a longer period. Your plants will appreciate the high light, they are more efficient than the algae and only need a few hours of it a day to thrive. Furthermore, I don't see any harm in having a few photoperiods a day, and I suspect it would benefit your plants, I understand your trying to replicate nature, but there is lots of algae out in nature too and lets face the facts, most natural systems don't have injected CO2! I set my photoperiod to be on only when I'm going to home to enjoy it, plus I'd just have all 4 bulbs on, I don't think the plants really care if it ramps up from 2 to 4 bulbs.