In the small BioCube the only option is the third/return pump chamber. The middle chamber has all the filter material and the first chamber has the heater. I did extend one the output of the chiller line so it would reach closer to the intake of the return pump. The intake of the chiller is a shorter line so it sits higher up in the chamber. So far things seem to be working just fine. I originally had the same concerns, but so far I think we are ok.
I made this change almost right away. I had the heater at 76 and the chiller set at 77 and it wasn't working. When I rated the chiller to 78 degrees it magically started working.
I made this change almost right away. I had the heater at 76 and the chiller set at 77 and it wasn't working. When I rated the chiller to 78 degrees it magically started working.