There is Tropical Lagoon, but they have never been very good.
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I have to disagree. I've never had problems with their stock, but they just don't carry much in the way of dry goods.
Also, Batfish Aquatics does have a brick & mortar location, it's just only open to the public during events or by appointment and isn't a traditional store.
There's also Congressional Aquarium in Rockville (I'm not a fan of their stock, health-wise) and Aquatic Creations on 355 north of Clarksburg (I think the area is called Hyattstown).
Aquarium Center was a sad story of a once glorious business run into the ground by a greedy owner, then sold to two poor guys right before the recession hit. Try as they might, they couldn't get it back on its feet.