Who keeps eating my peppermint shrimp.

[stingray]

Ok, I have a 75 reef gallon tank. I want to keep some shrimp - peppermint or cleaner shrimp. I started with peppermint because they are cheaper - plus they will eat aptasia. Something in my tank keeps eating them. I have tried about 4 shrimp. All gone. I only have two large green chromis and a 3-4" yellow tank. When I put the shrmip in the tank, the yellow tank went towards them and followed them around a little. But the shrimp went under a rock. They shrimp were about 1.5" Is the tang eating them?
I really want to keep shrimp, so I am also looking for suggestions on what fish to keep - that arent completely boring.

Thanks