First, recommend you join the local reef club. We’re very active, and I get all kinds of great deals on other people’s frags and equipment sales. You also get an excellent discounts at a number of sponsoring LFS’.
As far as stores, unfortunately most of the good ones are either by appointment only (with club discounts!), or over an hour away from the city center.
As far as shops which keep semi-regular hours:
I can heartily recommend blue ribbon Koi, an hour and a half away.
I also recommend ReefEscape in Fairfax, generally.
I can give a qualified recommendation for quantum reefs in Springfield.
House of Tropicals near BWI airport is an old-school fish store - in both the good and the bad sense.
Thank you for taking the time to reply with all that information. I will definitely join the local red club. I plan on finding s home near Arlington in order to be close to the Pentagon. Looking forward to the area and looking forward to start adding more fish and coral to my tank.