If you own a Emperor 400 you know this is a great filter but keeping up with the Filter Media is a pain you can pay as much as 18$ for a 4 pack well no more buy an extra set of optional trays seen here
http://store1.yimg.com/I/wetpetsusa_1856_4872503
Plus some Polly fiber seen here or similar
http://www.petsmart.com/media/ps/images/products/detail/large/i/inP0/inP036330large_f98f.jpg
And just place your favorite carbon in the first half of the tray and cut the right size strips for the other half and then lock the trays together and there you go cheap filter media
Got a cheap replacement for another filter post it here
http://store1.yimg.com/I/wetpetsusa_1856_4872503
Plus some Polly fiber seen here or similar
http://www.petsmart.com/media/ps/images/products/detail/large/i/inP0/inP036330large_f98f.jpg
And just place your favorite carbon in the first half of the tray and cut the right size strips for the other half and then lock the trays together and there you go cheap filter media
Got a cheap replacement for another filter post it here