I agree, the lights have been on too long, and possibly a bit too much wattage for no co2 or Excel, your nutrients have probably been depleted. If you bump the nutrients and cut the light way back, you should be able to find a balance at some point where uptake won't be so fast to require constant ferts. I personally would dose Excel daily with that much light.
Your carbon is probably exhausted by now and only serving as bio-media at this point, but in the future I would avoid adding carbon to a low tech tank since you'd possibly be robbing the plants of nutrients.
You don't have to worry about surface agitation if you're not injecting CO2, you have nothing to lose and could even improve conditions by increasing circulation with an airstone or whatever else.
Don't doubt the CO2, there is a balance where light should be limited by your CO2 ppm, your light seems to be limited by nothing but an overworked timer (or would it be 'under'worked?
). That doesn't mean adding CO2 is your only solution, you can just cut light to meet the balance.
Put a root tab under that sword, if you haven't already.