i've marked the openings... there is a grid along the top of the bio cartridge thats completely open at the top... when submerged the water can take the path of least resistance and flow up the side, over the top and straight down the middle...
i've marked the openings... there is a grid along the top of the bio cartridge thats completely open at the top... when submerged the water can take the path of least resistance and flow up the side, over the top and straight down the middle...
i built my own underwater internal filter out of a jiff peaute butter jar. i just drilled out the bottom, put a white plastic sink strainer there, drileld a hole in the lid for the powerhead and presto, i built a simple underwater filter. next, the thing was filled with bio max and filter floss. finally,i spray painted it black to blend it in.