I have this cpr sr3 skimmer that I have used for the last 2 months. It is the largest skimmer I could find to fit a bio cube. It fits in the middle chamber. $100
http://www.petsolutions.com/storefr...m_campaign=SR3ProteinSkimmerforOceanicBioCube
http://www.petsolutions.com/storefr...m_campaign=SR3ProteinSkimmerforOceanicBioCube