I have one in each of my three tanks . I have a BN pleco in each tank and they are little poop machines. I had the aquaclear 30 hob's on the tank and they weren't cutting it. We switched to the Penn Plax 400 internal cascade filters in each tank and what a difference it made . the water is clearer and I don't have to use the turkey baster most of the time now. I highly recommend them. They are so easy to use and clean. Alison