i have a penguin 350 that has an adjustable mid level intake and a lower level intake which seems pretty cool for filtration purposes. the problem is when i do a water change the filter will stop working when the water level falls below the mid level intake(which is suppose to be adjustable). even when i close the mid level intake the filter still doesnt act like a vacuum and suck the tank water from the lower intake. i think there is a flaw with this particular design. it seems like the adjustable level doesnt seal off the vents properly inorder for it to suck water from the lower intake. my concern is when the filter is not running it isn't circulating and oxygenating the tank water. also the bio wheels isn't turning which may lead to good bacteria colonies on it dying. how long can the fish live confortably while the filter isnt running(during gravel cleaning and removing old water)? what i do is every now and then ill cause a little bit of surface disturbance while cleaning the tank so my fish wont lack oxygen in their water. im also assuming when i replace the tank water the surface disturbance also oxygenate the water somewhat. also will the good bacteria colonies be affected negatively cuz the bio wheels is turning? how does this affect the tank during the cycling process? cant learn if ya dont ask so excuse me if im asking stupid questions.