Shrimp, otos. There isn't much you can keep in a 10g in the long term, even though people never get tired of trying. GBRs really like it warm (79°+), and there aren't many fish that like those temperature and will do okay in a small tank AND will get along with the ram. You could try a peaceful killifish species or maybe a goby if there are any that like warmer temps. Some guppies would work to and fill the space near the surface nicely.
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