PetStandard Premium Charcoal Filters for PetSafe Drinkwell Fountains, Pack of 10 (B00LCIV210) $9.22@ Amazon

https://www.amazon.com/dp/B00LCIV210?psc=1
Pack of 10 filters
Compatible with Drinkwell Original, Drinkwell Platinium, Drinkwell Big Dog, Drinkwell Multi-Tier, Drinkwell Outdoor Dog, Drinkwell Mini, Drinkwell Zen
Keep the water in your pet’s Drinkwell fountain tasting fresh
6 compartments evenly distribute charcoal for long-lasting filtration
Replace filter every 2 to 4 weeks