Lighting is indeed your problem.

You have very very low lighting and those plants will not do well without increasing your wattage. Even adding fertilizers will not help them IMO.
If you are on a budget, I suggest picking up 2 double shop lights, which will give you 160 watts over the tank. That should be enough for your Sword, which requires a tad more light than the Hygro. I suggest getting 40w bulbs that are in the K range of 6000-10000, as your 18,000K is above the plant spectrum. You may need to buy the bulbs at the LFS or online, but pay attention to the Kelvin (K) rating on them and don't go by what they say (for example: "plant bulb")....they aren't always the right K rating even though they say they are for plants.
If you can spend a little more (for better fixtures), then I suggest getting a T5 HO fixture like this one:
http://www.drsfostersmith.com/produc...0&pcatid=16770 or getting a compact fluorescent one that is 130 watts of light. The T5 HO fixture has higher light output, but the wattage is lower. I'd suggest that one, as its going to be cheaper than most 130w PC fixtures.
You will need to get a new fixture to get more wattage. You won't find bulbs higher than 40w for your fixture.
I suggest you upgrade soon, as your plants are going to continue to deteriorate without more light.
Once you get more light, then we can talk about nutrients. Dosing nutrients will not harm the fish. Once you get more light, your plants will need more nutrients. Seachem Flourish is good for the small micro nutrients. I wouldn't get it just yet though.