Landlords are entitled to general cleaning fees and if there is carpet, for professional cleaning of the carpet, which is how the carpet should have been when you moved in. You are expected to return the unit in a like condition. If you think there should be ANY wear and tear in just six months, then there is something wrong with you. Think again. Normal wear & tear takes YEARS. I cannot think of ANYTHING that would be considerably worn down or worn out after just six months. He can call the security deposit a risk fee if he wants to. Any way you look at it, he is entitled to use it for the cleaning and for any damages sustained while you rented there. If the fee you paid does not cover it all, expect to be sued for the balance owing. If it covered it and there is left over money, in most states, if not all, he must refund you the balance. The time allotted varies from state to state but you are likely due some refund if there is money left. Where he can keep it and not refund it - I don't know.
Certified Paralegal, with 25+ years' experience & with Landlord & Tenant law experience.