I got some hardy, low light plants (basically water sprites) recently, and they are browning and look like they are dying off. My lighting is adequate (40W fluorescent bulb for a 5.5G tank), and I have flourish tabs in the gravel (it's about 3mm in size) and use small daily doses of flourish for trace nutrients. I think the problem may be the gravel. I read that gravel that isn't "lime-free" can cause problems, and the gravel I have doesn't specifically say that it is lime-free, but I'm not sure if this can be an issue big enough to cause dying plants. I also have a couple of java ferns attached to a piece of driftwood that are doing fine, which also makes me suspect that the gravel is the problem. Can it be? And if not, what could be the problem?