I have a 75 gal tank, with the standard light on it. I don't remeber the watts, it's the one that came with the tank hood. Anyway, I went and bought a bunch of low light plants from that fish place that pet place. They have been doing okay, and only once or twice have been found floating. But last night I noticed that some of them, mostly ones with broarder leaves are turning brown in spots. Not brown like dying, but dark brown. SO, my ? is will/should I get some plant food type stuff or what can I do to help my plants grow and thrive. If it matters, they are in a sand substraute. What I did when I set up the tank was to put a punch of small rocks around their roots, then a few bigger ones, lastly came in and filled the rest of the tank with sand. I thought the rocks might help keep the roots from being compacted by the sand.