I have this old junk tank that i decided to clean up. its only 10 gallons. i threw in some java fern and low light plants and started to fertilize with iron and flourish. I have cheap Shultz Aquatic SOil. Im not sure if that stuff has anything in it other than beign gravel. what can i do to add more iron into the gravel? is there any kind of cheap plant tabs or something like that? i don't think i will be tearing this tank apart and redoing it, so a better substrate is not possible. my mother doesn't want me to spend too much time on this.