I was curious what anyone thinks why I have a small issue with a little gunk on some of my air tubing in my RDWC. My water temps are cold enough around 69, plenty of oxygen and water circulation. My roots are excellent. I generally see the shit under the lid of my containers with the portion of the tubing not exerted into the water. I have sense made sure my water levels remain higher. I also use H202 to help keep the system clean. Would there be any other reason anyone could think of besides what I just mentioned related to the water level being a bit to low? Exposing some tubing as well as some of the root matter? Perhaps creating humidity directly under the lid? Like I said sense I have made sure the water level remains higher things seem to be clearing up. Any thoughts? Thanks for your input