I would say by the rounded shape of the tips, actually not acropora, but more of a Humilis or Millipora. Basically the same as an acropora, but the body looks a bit different to me. Most acros will have a thinner top growth even the same for Millis. Its why I say Humilis. They are very demanding of light. Everytime I frag mine the whole colony turns brown for a week then goes back to a nice purple, red, and blue with green polyps. Same body style tho. Good find