I planted out my new tank a few days ago...but no matter what I do quite a few of the plants refuse to stay in the gravel...I get it looking great, and sure enough, when I come back later there they are floating at the top of the tank. It's driving me crazy !!! I've read that a strip of lead can be used to weigh down the plants...but surely lead is quite a toxic substance. Could it, over time, leach out into the water and harm my fish...or is it inert in its solid form ?