I think that it is a juvenile akindynos (as certain as you can be making an ID from a grainy photo - much better to have the fish in hand).
I had never seen a juvenile akindynos until earlier this year - all the adults I have had over the years had bright white tails. This young fish arrived with that same dusky patch on its caudal fin that the one in the picture shows, and now 6 months later, its tail has turned bright white. I think that the light colored mask on the face is also diagnostic.
Jay