I just got a Tetra water pump (325) and the Tetra Submersible Flat Box Filter for my 150 goldfish pond... but I'm a little lost on the connections. As I understand, I connect the black corrugated hose to the only connection that fits on the box filter, and then that tube to another connection on the side of the pump itself (under that removable plastic thing, right? What is that for, if I can't leave it on?) using another connector bit? But then what about the hole on the top of the pump, if I'm not planning to put a fountain or anything? Is it OK to leave open? Thanks for your advice! I kinda guessed this from the videos on the Tetra website, but it only shows it with a fountain or other thing on top, so I wasn't sure.