Hi there, currently I have a jewel rekord 70 and rio 300. I love the make and the set ups I'm running. However, the filter mediums are sooooooooo expensive. So I'm wondering, what can I do to cut the cost while still maintaining good water quality? This applies more to the rio 300, which is been re-scaped as a planted biotope aquarium. One thing I have considered is using jewel/other filter wool at the bottom and top, while inbetween having lava rocks (I'm guessing that since thier pourus they'l perform the same action as the filters), and activated carbon...and alot of plants. Does anyone know if this will work?