I bought a usb air pump to pair with this, and it’s literally GUSHING water out of the filter tube. I’m overjoyed because that means it’s filtering the aquarium water at a very fast rate. I have an older sponge filter like this one with only a single head, and it’s always sputtering water or spewing very little water. However, I know it works well because it’s always dirty whenever I squeeze it out each month. I bought this bigger one primarily to replace another sponge filter of a different type that has a tube that goes out the center of a single big sponge. It sits on the bottom of the fish tank instead of being suctioned to the wall. I didn’t like that one because the pores of its sponge were too big, which prevented it from sucking up all of the micro-poo pieces from my goldfish that ends up clouding the water. I know this because during cleaning time, it was less dirty than my other single-head sponge filter even though it had a much bigger sponge. Therefore, I prefer these tube-like sponge filters more. It also saves a lot more space for my goldfish to swim in and is taller at the same time!