I have a 9004 and a 9001. The 9001 never gets used because if there is any flow at all near it it bleeds microbubbles into the tank. I put it into my cube (12x12) and no matter where else i placed my mp10 or how low i turned it, it was still too much flow. The 9004 on the other hand is great. Good surface skimming and not too temperamental when it comes to water level as long as its flowing into the surface skimmer. The 9001 takes up a good amount of room if you put the surface skimming attachment on it as well. I like Tunze products, but regret purchasing the 9001.
