Sword plants are often listed as low light, but they really do like light. Sounds like you're doing DIY CO2 on a 55 gallon aquarium?
It's not impossible, but tough to pull off. I'd say 2 bps is likely not anywhere near the amount of CO2 your tank wants.
Growing plants is not difficult. It's more or less the same with almost every plan. Give light, carbon, and NPK with micros, and everything will grow.
Sword plants are easy to grow, but they need the aforementioned conditions. Don't get so hung up on iron. Plants need it, but nitrogen (low nitrates can be an issue), potassium (especially important), and phosphorous are much more important.
It depends what kind of lighting you have, but if it's T5HO lighting at 4wpg, that's enough light to grow sunburns. With that amount of light, nutrients become extra important, and Flourish won't be able to provide what is needed at the recommended dose.