I have a starter I use twice a week. It's doubling when I feed it and turning out tasty loaves. The only thing is it's started "drying out" between feedings. I use it twice a week as I said, and feed it both the day before I plan to use it and also the day I use it, so I'm feeding it at least 4 times a week. It sits on the counter in a glass canning jar (the kind with a glass lid, rubber gasket seal) in the meantime. It's not particularily dry or humid where I live and heat is a comfortable room temp. On days when I don't feed it, it gets a dry skin on top.
Should I be concerned?