55 Gallon planted - Advice please!

[AquaView]

I need a little bit of help! My HC 'cuba' is not growing fast at all. I have had it for a few months and only a few runners. Some of the leaves turn a dark green and don't look as healthy as the others. How can I speed up growth in my 'cuba' plants as well as all my others????

Another thing, I do not like the look of the roots coming out the sides of the stem on my Ludwigia repens, and Water Wisteria, is it safe to trim them all off??

Plants: HC 'cuba,' Water Wisteria, Ludwigia repens, Rotala macrandra, Dwarf water trumpet (Cryptocornyne wendtii), and a dwarf lily

Lighting: Coralife 4 bulbs 65 watts each, 6700k (9.5 hours per day)

Compressed CO2: 2 bubbles per second. The Diffuser is placed under the filter
intake.

Filter: FilStar XP3 Canister Filter - 350 gph. No charcoal, extra bio-balls
Some surface agitation

Substrate : "Red Sea" flora base

Fertilizers: Flourish nitrogen, potassium, phosphorus(half dose), Iron, Trace every 6
days, Off setting every 6 days I add Flourish Comprehensive so
basically every 3 days I'm adding fertilizer. (Following directions
bottle)

Water: Every 3 days I change about 6-8 gallons. (Tap water with conditioner)
pH sits around 6.6-6.8, Temp is at 78F. GH-0 ppm, KH- 40ppm,
nitrate 5ppm, nitrite 0, ammonia 0

Inhabitants: 8 amano shrimp, 10 neon tetra, 2 congo tetra, 3 SAE, 3 clown
loaches, 1 siamese fighting fish(male), 1 aquatic frog.