wow you have frontosa's in a 55g. I don't wanna start a fight but I would hope that this is just for growout. those things get big.
My first opinion is that I'm not big on a african cichlid planted tank. it just doesn't seem natural. but that's probably just me. I'm used to american and south american cichlids in planted tanks, but not africans.
To get better plant growth...I'd have to say that better light is a must...but again it's not cheap. I mostly buy my lights from TriCityTropical.com, they sell refurbished items. Both my big lights came from them and they were at least 50% of brand new cost. So I saved a bunch, but they were still not cheap. And the CO2 is a must...but you seem to have a little of that already.