Wonderful World of Fish - 28th St, Steinway St Astoria Nice selection of salt and friendly and knowledgeable staff.
Seavision - Astoria Blvd close to 23rd St - last time I was there the tanks were half empty. Can't say it's a good thing or bad thing.
Coral Aquarium - 75th, St Roosevelt Ave Woodside - Been there forever and a day with limited selection but good advice.
Haven't been to Coral Aquarium in years....last few times I got things from there, I had to acclimate things forever...they keep (or at the time, kept), their tanks at brackish levels....I think the sg was 1.019? Maybe lower...even with long acclimation, that puts too much stress on your livestock.