Well my buddy finally broke down and bought a tank. He got a Penguin 350 for a filter only problem is.... Neither of us know probably the dumbest question to have ever been asked.... On the mid intake for the highest filtration(GPH) does it need to be opened or closed? He just texted to ask me and I have no idea? I thought opened to suck in more water but then that could also just be to release water to lower the GPH? So I'm puzzled