Actually I just pushed it out w/my hand. I was amazed how easy that thing came out. I am guessing it was in there to act as a floor for the filter that came with it.
I put my heater in Chamber 1 and kept the filter in there for grins. Going to put a skimmer in Chamber 2. Then upgrade the pump in Chamber 3.
From what I understand, once you bag the bio balls, you can then fill up Chamber 3 and not be bound by the min/max lines.
Dave