This is your apartment so it is up to you to decide what is reasonable. There are specific laws associated with how you keep the security deposit. It may have to be placed in an interest bearing account/ in escrow during the rental period. Therefore do your homework.
I have seen instances where landlords charge 2 months security plus additional security for other items such as pets or a pool as these could cause damage or need to be maintained.
I would check your local magistrate to determine what rules you need to comply with.