CO2 and ferts aren't necessary if you've got a nutrient sponge like H. difformis. The 20g in my livingroom is sitting around with eco complete and a 60w CF, but no CO2. There is bacopa caroliniana and hygrophila difformis in it right now. Algae is pretty minimal.
DO NOT add phosphate unless you know what you're doing. Phosphate promotes algae growth far more than it helps plants IME. It's the whole interphase vs. mitosis thing. Algae spends a far higher ammount of time in mitosis. Phosphate comes in through fish food, decomposing plants, and the local water supply if you're using tap water. Get a test kit for phosphate first; if it's zero before a water change, then consider adding it. Otherwise it'll just feed the algae.
Seachem's "Flourish Excel" is the one that's got the biggest reputation. In some cases, it's helped to knock back algae levels. Looking through a 2002 issue of TFH, I see ammano was using ferts labled as, "Brighty K", "Green Brighty STEP 2" and "ECA" All ADA products. They're $20 a bottle, and pushing a higher light system would probably be needed to get things right.
I guess it all comes down to how much money you want to blow on test kits , ferts and lighting vs. how much time you're going to spend waiting for plants to grow and using trial and error.