How Much / What Kind of Fertilizer

My green plants have a slight case of the yellows - Iron and Potassium I guess. Right now I use Flourish every three days. Doesn't seem to be helping - the old leaves are turning a bit yellow and the new ones are coming in a very light greenish yellow. Java Fern and Anubias mainly. I change water once or twice a week. Setup is 3.8 watts per gallon, 2 fluval 305s, CO2 with a ladder, ph of 7, kh of 8 and 0 ammonia.

btw - the red plants in the tank look great!

sweet ... thanks so much!