how big are the ST and angel? datnoids are usually well mannered fish when it comes to fish about there size or bigger. ive kept my baby indos with angel fish a little bigger and they did ok.
I had two silver Datnoids (D. quadrifasciatus) about 4" with two albino Angels that were about half grown or about 3-4" high. They got along ok for a few weeks but then the Dats started to pick on the Angels and the two had to be seperated. Still have the Angels but sadly the Dats died about six months ago when I was out of town for two weeks.