think it might be better to integrate the fertilizer into your substrate. there are many different ways to do this... some people use laterite, vemiculite, various clays. the easiest thing IMO would be to use a substrate which is made for planted aquarium like Seachem Flourite. be careful when using liquid additives so you aren't feeding algae instead of plants. there are many options for fertilizing plants, best thing i can tell you is do some research via google. there are lots of variables depending on what you want -- required lighting, co2 injection etc.