I have. 37 gallon tank with a TopFin 40 corner filter. I have added a large sponge filter in the opposite corner which is conveniently hidden by a large pogostemon octopus. I am currently stuffing my corner filter to the brim with a bag of Purigen, Sponge and filter floss. My question is: if I use Purigen do I also need the sponge and filter floss? Or am I stuffing my filter and probably impeding the flow for no reason. Your help is appreciated.