Comparison : Item # E5328, E- Series 2.5 X 6" granular activated carbon
Item # E5385, E- Series 2.5 X 6" all polyphosphate
Item # E5320, E- Series 2.5 X 6" 1 micron carbon block
Item # E5320-P, E- Series 2.5 X 6" 1 micron carbon block with polyphosphate
Item # E5485, E- Series 2.5 X 8" all polyphosphate