I run a Tunze 9002 in my second chamber. You have to do some plasti trimming on the inside to make it fit but it works great. Very sensitive to water level, however. The Sapphire skimmer available at nanotuners also gets goods reviews and will fit with no mods. If I had to do it all over again, I would go topless, get a 20" sunpod MH or nova extreme pro T5 a get a decent HOB skimmer like the AquaC Remora or Deltec MCE300 (supposed to be the best but expensive).