Good information thanks all. I have always kept mine covered with water, feed them morning and again at night, then add more about every other day. It is usually bubbly by morning after adding new food.
Kassaundra has been doing this for almost 3 years. I ask her why she kept hers covered with water and she said she learned it this way so never deviated. I hate the thought of having to drain so I don't. Do both ways work. Yes, of course. Personal preference. IMO