I've always ordered the impellors directly on line from the Rio suppliers--I think I've usually used "Greystone," but always have to do a new search for Rio pumps every time I re-order because I can never remember the exact site URL. Once in awhile they are out of stock for impellors, so with the amount of tanks I have, I keep some extra pumps and impellors on hand. I've never looked for them in a pet store, since I'm in a remote location and do most of this kind of shopping on line. For me, the shipping costs are less than a 150 mile drive to the nearest pet store, especially since I always order several things at one time. But for you, if you're close to a PetCo or PetSmart, you might ask them to order for you if they don't have them on hand.
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Patty
Pahsimeroi, Idaho
4 D. auratus blue
5 D. galactonotus pumpkin orange splash back
7 D. imitator
6 D. leucomelas
4 D. pumilio Bastimentos
4 D. fantasticus
6 P. terribilis mint and organe
4 D. reticulatus
4 D. castaneoticus
2 D. azureus
4 P vittatus
2 P. lugubris