I have mine in small bark. It seems to work, they flower on my windowsill at home, in pitifully low light. They do dry out quickly, and I soak them twice a week.

Most people use a bark mixture and the smaller the medium, the more it will hold moisture. Keep in mind that bark will break down and deteriorate in a couple of years. The speed in which it breaks down is determined by the size of the medium and it's environment. The smaller the bark, the faster it will break down.

Place a plastic tag inside (on the side) of the pot and mark the date when you replaced the medium. I would check it once a year, and more often if you begin to see signs of trouble .. other than scales and insects.

Usually, if there are no physical evidence of what's causing the problem other than lack of water which will be evident by wrinkled leaves, then it's time for some serious investigation. Normally it starts underneath in the root zone area.

Please note that wrinkled leaves doesn't always mean lack of water, so if you think you're doing everything right and you're losing leaves right and left ... then it's time to act.

One important thing to note is the medium that is currently being used. If the orchid is doing well, then seriously consider using the same medium. Sometimes, changing the environment will seriously impact it's growing condition. JMO

I have had really good results with the Paph mix from Robert's flower supply. The mix has small fir bark, turface, humus, sponge rock, and vermiculite.