"lots of iron" is a very very bad thing. Too much iron will cause the plant to turn yellow, wilt and die.
You need to get a Flourish Tablet (comes in a 18 package, 1 tablet every 3 months, last over 18 months for about $6.00). You place the tablet into the gravel, about 2" down.
Liquid fertilizer I never use. You need a tablet that releases itself over time or as to the plants' needs. The rest of the fertilizer will come from the fish poop. People do not realize that fish poop itself can make up for 75% or more of the fertilizering in the tank.
I never have used CO2 (and never will), but you can try this. My advice is against it...you need to go as natural as possible.
Flourish tablet plus fish poop, way to go.
One last thing, make sure you clip and toss out all dead leaves, or else the dead leaves will starve the other plants or the plant itself of nutrients for it will attempt to heal the dead part or the dying back of the dying eaf, and cause to rob the rest of the plant the proper nutrients; also, dead leaves or even dying back leaves create bacteria.
You may also want to pick up some Olive Nerite Snails which do not produce live snails, only eggs which never hatch in freshwater, these snails will clean the leaves of all your plants, thereby opening up their pores which get clogged by dirt, etc.
hope this helps