It's not a Tang, it's Malawian, a hap, Not Aristocrhimis christyi or D. compressiceps.
A. christyi has somewhat of a black bar that runs immediately under the dorsal, touching the base of that fin. The second, the one that is so apparent in our unidentified hap, is slightly more curved in C. christyi - away from the first line. Not characteristics I'm seeing the the unID'd fish..