These replacement filters are for the EX line of Tetra Whisper filters. These are not the same as the Tetra Bio-Bags! The best way to tell the difference is that the EX line of filter pads have a rounded bottom and fit into a clam shell frame. The Bio-Bag filter replacements have a square bottom and the frame goes on the inside of the filter bag. The Whisper Bio-Bag filter cartridges can be found here.
Medium Carbon Filters fit into the Whisper EX20 only!
Large Carbon Filters fit into Whisper EX30, EX45, and EX70