I use Penguin filters for all my fish tanks , and standardize the size of filter pads I cut from polyester batting I bought from JoAnne Fabric. I use the cages to hold the DIY filter pads for less than 5c each pair. My 125g run on three Penguin 350, and 75g on two 350 that are sufficient to keep the water crystal clear and quieter than my HVAC. I never use carbon nor bio rings in the cages, but there is room in front of the cage to insert a foam for additional bio if needed
I never use carbon or extra biomedia either. Any surfaces (substrate, rock , plant and glass surfaces) are bio media and all you need to provide is oxygenated water. So good water movement to promote gas exchange is essential not just for bio, but for plants too. I do care for crystal clear water for my enjoyment so mechanical filtration is as important to me as good water movement.
