1394 Surefit Cartridge for Dynaflo I, Millennium 1000, others 4pack, PennPlax Fits Drinkwell fountain. These cartridges contain zeolite and carbon, and are not a bad cartridge. I do not know how important ammonia removal is to a cat, but that is what the zeolite does. And most tap water contains ammonia. No customer feedback as yet, although we sent out a free pack of these with the Blueline cartridges when we first introduced them.