Minecraft wiki entry for Axolotl_farming, associated text: If the spawning room is below level Y=30, the conditions that cause axolotls to spawn also cause glow squid to spawn. Because axolotls kill squid, you can arrange the farm so that the glow ink sacs dropped by the squid are swept into a collection chest. Or if you don't care about glow ink sacs, you can make the farm even simpler by ignoring them; the ink sacs disappear after 5 minutes.