Newbie looking for advice

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She would consider the 'purple' rock to be premium because it's covered in coralline algae (that's where the purple comes from), instead of being bare. I'd actually recommend buying a mixture of different rock types from different stores; you get a nice mixture of organisms coming in on the rock that way.
Look for miniature fan worms and the like; they'll spread to the rest of the rock once you have them in your tank.