Pretty much self explanatory, I noticed it right now when I was getting ready for a water change. Its at the top part where the water doesn't touch it. should I be worried or is this just good bacteria?
Unless it is a soap or detergent residue, I wouldn't worry too much about it. I've read other threads in the past about white foam, and I can't remember what the responses were, but I seem to remember it not being a problem.