I live out east in Suffolk in Riverhead. There are 2 stores 10 miles west of here but none east of them.
One place is filthy but has been there 50 years and is the place I go to. I am going there today. His prices are about a third of any other place on Long Island or anywhere else. Good selection but has no phone. Like, yeah, I know.
That is Aqua Hut in Coram.
Another place is on the same road (112) in Patchogue. Much bigger and cleaner (although they are doing renovation now and changing all their tanks so not much there this week)
Prices are high there but they can probably answer your questions. It's called "Pets something". But in Patchogue.
Another brand new place opened last year in Patchogue. Beautiful place but expensive and I have not been there in 2 years so don't know if it is still there.