How fast can I raise rent?

[Preston Quinn]

Ok, I have a deal that I’m working on. It’s a nice brick duplex that is currently rented for $525 per unit. On rentometer, in a one mile radius the average rent is $728 for a 2/1. The asking price is $135,000. I feel like I would need to spend $5k in this property to get market rent. The tenants in the property have been there for 7 and 10 years. I’m assuming due to low rates. They are on a month to month lease. 

My question is this, in Virginia how much and how fast can I raise the rates? I realize that I could potentially risk losing the tenants if I move to fast. But what are the laws on this in Virginia?