if you own an emperor filter and you don't like the cost of repacement cartridges,try this.take a hobby knife or razor blade,shave off the old polyfiber and go but tetra pro 2 media bags and slip them over the old cartridge and fill with carbon like normal.the cost of the emperor carts.is around 9 dollars for 2.the cost for the tetra replacements,11 dollars for 4.i like my emperor but the cost of upkeep sure can be high.with this solution i can do pad changes as offten as i like without the high overhead or odd fitting alternitaves