ok i just got my 2 emperor 400s up and running and on each filter one bio wheel is turning fast and the other is hardly moving. on the side thats turning fast there are 2 filter things behind it, on the side turning slow its empty behind it. im just wondering if this is being caused by that one side not having anything behind it and if that it why do i need to put filters there like on the other side. PLZ help me with this, im new to this hobby and kinda lost lol. thank you!