I know what you're feeling because I was there not long ago (still am when it comes to other problems). There are variety of things you need to take into account. Before I list off a few, there are a couple of websites you can look to get some more information on the overall aspect of planted tank.
www.rexgrigg.com http://www.thekrib.com/Plants/
These websites will provide you with a whole lot of information to start.
Now on to your tank: One thing I noticed is that you didn't mention what substrate you used. While its not the most important factor, one thing you do want to worry about is the size of the substrates. Smaller grain/particles are much better than large gravel/pebbles. Not to say its not possible because i'm sure someone here has had success with the larger gravel, but it may be easier to go with a smaller size. There are many choices and all require some researching (eco-complete, flourish, SMS/turface, sand, etc)
Your lighting needs to have a better selection of bulb (if I am assuming correctly, the 50/50 is the actinic and white bulb right?). As long as the K range is between 6000-10000K the bulb should be ok (However, this is misleading because it is the color spectrum that is more important that the K rating)
A large tank like that, unfortunatly, requires CO2 if you have high lighting. You didn't mention how much wattage your lighing is but I'm going to take a wild guess and say its 130W. That's just about at 2wpg and depending on who you talk to, may be borderline for CO2. Necessary: no; beneficial, yes
Ferts: I think this is your biggest problem because you only mention using flourish. Flourish is a "micro/trace" fert and you need all the macros to supplement that. They include Nitrogen, Potassium, and Phosphate. Seachem has all 3 as well as rex grigg (in a powder format).
I don't think the activated carbon is a good idea so I would simply remove.
Hope this isn't too much at once but you will get the hang of it. I simply read and read and read to get a better understanding. Don't be afraid to use the search function because you will get answers faster that way but also don't be afraid to ask a specific question either. Hope this helps...