Can you give us a little more information about your tank?
What type and how many lights do you have?
How long are they on for?
Has anything changed about your lights recently?
Has anything about your fish load changed recently?
It looks like you're using gravel for your substrate, right?
It's a little interesting that everything has been good for a year and now is starting to decline, which is why I wonder if anything has changed.
So it looks like you're adding all these things from the Flourish line; Trace, Iron, Comprehensive, yes? If you are dosing all of those, your plants are getting all the type of nutrients they need, but probably not enough and not likely in the right proportions.
You said CO2; do you mean you're dosing Excel, or that you're injecting CO2 gas?
I don't know how much you know about plant fertilizers, but I'll try to give a quick run down. Plants need 3 macronutrients in large amounts: Nitrogen (N), Potassium (K), and Phosphate (P). They also need small amounts of several micronutrients.
Comprehensive is supplying N P K and most of the essential micronutrients, but like I said probably not enough. If I were you I would keep dosing with your Flourish supplies until you use them up and look into dry fertilizers because they are exponentially less expensive.
You can buy dry fertilizers at sites like these: http://greenleafaquariums.com/aquarium-fertilizer.html
You'll need to get KNO3 (supplies N and K), KH2PO4 (supplies P and K), and a source for micronutrients (I use GH booster). In a planted tank ideal nitrate levels are 10-20 ppm.
How much you dose will depend on how high your light is.
I hope that helps more than it confuses, and feel free to ask questions.
Hopefully someone else might be able to see if they recognize the specific symptoms of your plants to confirm my hypothesis.