I've been told that black spots on my java fern is from lack of nitrates. I'm wondering how to get them to rise to an ideal amount? My 55 gal is 0's across the board using API master kit. Every Saturday I use the recommended amount of API leaf zone and every morning I add co2 booster from API. I've got around 17 varying species of fish in there and the substrate is sand. Also - I use the two t-5 lights, one white , one with a hint of pink. 6700k spectrum I believe. Help would be awesome as my sword looks like its getting black spots and turning a ugly dark green on the outer, but has nice good growth from the center. Thanks ahead guys!