Feliway Multicat Diffuser Refill 2 Refills 48ml Each

Can you use this with hepa air filter machine in main room that cats are in?

What is the expiration date on this?

I used these last month and they were great. This month, one of them was almost gone after just 10 days. Why?

What's the difference between single cat diffusers and multi cat defusers?