Haven't Closed yet. When do I raise rent?

[Michael Healy]

I am in the process of buying a rental property with a tenant already in it. Getting it at a very good price, but I believe the rent to be low. Its at $998 when I think it could be $100 to $200 a month low. The tenant is section 8. This is my first rental, so I'm wondering when I should request a rent increase. Any help would be greatly appreciated. THANK YOU!