Pet deposit mid lease?

[Lindsay Repp]

I just closed on my first deal in mid July on a fourplex and the building is full and has been for the most part since I discovered it. Although during the process of closing one of the tenants (month to month) acquires 2 cats. I didn't plan on allowing pets without a separate deposit. Am I able to notify him that I will need a deposit for the pets in the middle of his lease? Has anyone experienced this?