I feed mine shrimp and silverside. I had a nem before and two of my shrimp and a fish got to close for comfort and got ate right in front of my eyes two different time, nothing I could have done because once in those tentacles it's over.
You could add more rocks and if you do try adding the amount you want at one time because each time you do your water will start to cycle all over again. I would not add any more damels if I were you because sometime their will not get along with other fish when you are ready to add more.