I moved into a new apartment recently and my cat has a cat friend now (he's 5, she's 1). I got him a new pine pellet litter after the move but before the new cat moved in. I mixed it in little by little with his usual odour buster clay litter, and he took to it well, using the litter like usual. The cat came here after some time, before I had to change the litterbox's contents over. At this time, the new cat (Boo) had her litter in my roommate's room, and she mostly stayed in there, and they weren't friendly. They got friendly soon though, and Boo's litter was moved to the bathroom with Lux's. Around this time I had changed Lux's (my cat's) litter to solely the pellet one. Boo was using the pellet one too. Lux pooped in her box but not in his. My roommate thought it would deter him from using her litter only if they had different litters, and also Boo pooped on the floor, so it seemed she prefers the clay. She has a clay one now, and Lux just poops in her box and goes there but not in his! They are really friendly together but it seems they should be using their respective litters? How can I get him to use his own? Help would be appreciated.