I would check to see if the level of water in the pump compartment is sufficient. There could be something dirty blocking or slowing the flow to this chamber.
Do you clean the sponge regularly?
I would also take the pump out and clean it for the same reason.
I had my wife clean the filter for me (on a 72hr shift) and now its working better from what she has told me. I have never pulled the pump. does it just slide out?? the instructions that come with the nano are a joke.
I would think it's a water level issue. The first day I had my aquapod, it was doing the same thing. I filled the water up to the max line and that seemed to fix it. Also make sure your filter is pushed down below the skim line. I'd pull on the clear hose that goes to the return jets and pull the pump up a bit and see if the hosing and pump are okay. Good luck with it.
to remove the pump, pull off the tubing from the output nozzle that plugs into the output on the black wall. Then just pull up with the hose and the pump should raise as you pull up on the hose. you may have to wiggle the pump alittle to get it out of the chamber