I have 2 Kentia palms in a conservatory. They are about 5-6 ft in height. They are in pots which have a water reservoir that you top up when the water level gets low. The leaves have started to go completely brown and shrivel. This has affected both plants and has happened to almost all of the leaves. I have read articles and books but don't know whether the plant is too dry or too wet or what the problem is. Can you help please?