I had a clownfish in with mine when I had my 20gal and they did fine together. I am sure you can add gobby's or firefish or blenny's. You might be able to add 2 bangii cardinals. I wouldn't add more than 1 or 2 fish depending on the size. And, without a doubt, keep a close eye on your water and make sure he is eating. you will need to observe them eating to be sure. They don't have a very long life in captivity. I wish you luck though, they are gorgeous.
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