Well I have a 10 gallon planted tank with red cherry shrimp. I have a DIY Co2 system set up. I have the bottle with the mixture with a tub to a gas separator. The tube from the mixture goes almost to the bottom of the bottle. The tube that goes to the tank is close to the top. It them goes to the CO2 ladder. This is where the growth is. Its at the exit of the tube, and on the bottom rung of the ladder. It effects the bubbles as the get disrupted and get knowcked off the ladder. It is white, kind of translucent. It only grows when the Co2 is present. I had trouble with the reactor for a few weeks and didnt have any co2, it was fine. I started it up and within a few days the growth was back. Does anyone have any clue to what it is or how I can fix it? I have had this exact set up befor on the same tank, a few years back and i never had this problem......