I think when I had my LB in water I was changing it about once a week. More often is probably better as it will replenish the disolved oxygen in the water.

I'm not quite sure what you mean about the leaves looking dry. The very tips of my plants leaves sometimes dry and brown a little, but I think that is only because the air is a tad drier than the plant wants. If that is the issue you can try misting around the plant.

Are you using TAP WATER? Flouride will cause the leaves to turn color and eventually kill it.