There is much debate on whether its better to have the skimmer before or after the refugium. I've ran both setups. My old sump only could accommodate the skimmer after the fuge and it ran fine. My current sump can only accommodate my skimmer before the fuge, and it's running fine and i'm pulling out excess chaeto weekly. In my honest opinion I don't believe either way is wrong. It's basically fit the skimmer where you can.