I'm trying to make a slime farm, but I can't get slimes to spawn. I've found the Slime chucks, I'm below level 40, I have a 3 high room, I know it's a slime chuck because when I place a mob spawner to place slimes they spawn, the spawner does nothing in a no-slime chuck.
Do slimes need anything else to spawn other than under 40, and in a 3 high room?