Westbery, your welcome. My name is Ric, my screen name is RJohn. I am also called Santa Ric. I think I am going to add a 6 inch deep sandbed in the middle chamber with some cheato. I have always had a nitrate problem. If it helps, the middle chamber is exacly 9 inches wide. The 3rd chamber is 10.5 inches with thebaffles, return pump and phosphate reactor. The first chamber is 11 inches and has my skimmer and the outflow. If I was making this from scratch, I would plan on the chamber with the skimmer being at least 12 or 13 inches.