Definitely get some vals for the background. I'm not sure but with all my low tech tanks i don't dose many ferts. Your plants aren't growing as fast as they would in a high tech setup and probably aren't using all those ferts. i have a 29 gallon with no CO2 and med light and only dose flourish once a week with water change also have a few Red clay root tabs under my swords and crypts and everything is growing quite well. In my experience Sags seems to be a slow grower in low tech setups. You might also try adding some Crypts or Moss they also grow well under low lights. Most stem plants don't do very well under low light conditions either they grow tall and lose all there lower leaves if they survive at all.