Fountain filters typically carry two-to-four-week intervals, shortened for multi-cat or heavy-shedding homes, guided by the manual and actual water condition.
The overlooked issue is biofilm: the slick layer on pump impellers, channels, and walls is a bacterial colony, so replacing filters without dismantling the pump cleans nothing.
Fully disassemble and wash the pump and all parts weekly, change filters on schedule, and keep water levels up to prevent dry-running heat.
Floating hair, odor, or a cat suddenly avoiding the fountain are wash signals; some cats prefer still water, and multiple bowls work just as well.
