Living in the same area, I can say that East Coast Aquatics is a good store, but there are plenty of others around that I would also consider good.
You should be less than an hour from The Hidden Reef. See them here (offsite) -
Welcome to Hidden Reef!
You should also be close to World Wide Aquarium. I consider them more a FW store, but they do have some SW items. See them here (offsite) -
World Wide Aquarium and Pets
If you don't mind crossing into NJ, The Aquarium Center is also good. See them here (offsite) -
Home - Aquarium Center, Inc.
If you don't mind going a bit north to the Allentown area, Something Fishy is also a good store. See them here (offsite) -
Something Fishy
If you are willing to make a day trip out of it, you are within driving range of That Fish Place in Centerville PA. See them here (offsite) -
Aquarium Supplies, Pet Supplies and Pond Supplies by That Fish Place - That Pet Place
Another day trip but extremely rewarding is a trip to Pacific East Aquaculture in Mardela Springs MD. See them here (offsite) -
Welcome to Pacific East Aquaculture
Now that you people from south eastern PA have plenty of stores to visit, with lots of equipment, supplies, and livestock available, so I'm expecting great things from all your aquarium systems. :laughroll