| | Re: sand or something else?
Sand does not hold nutrients the way better substrates will. It has not cationic exchange capacity.
Lucky Bamboo is not fully aquatic. It seems to do fine with the roots and some stem in the water, leaves out of the water.
If the Baby Tears is on a rock will it reach the substrate at all? I suppose ultimately it will, so I would select a fairly fine substrate that holds nutrients better than sand.