B2L2

If your tenant ask you to reimburse the filter cost, I think you will need to pay for it.

Rental unit that allows pet is actually hard to find and usually cost more.  I'm a dog owner myself, so I'm not against pet.  But don't underestimate what damage a dog could do to your apartment.  My friend's dog once dig a hole thru a drywall in a day.  Of course he need to repair that before he moved out his rental apartment.