Aequidens ID

With diadema the mid body spot sits above the dark horizontal line (band),
with pallidus that spot also sits but also stretches above the horizontal line, but the small spot on the gill plate is reminiscent of pallidus, and it could be (due to age) that those type distinctive characteristics, have yet to develop.

Metae, the spot is in line with the band, so a possibility, but on metal the marking on the gill plate is more elongate(?).
sp Atabapo is also a possibility, as per where the mid body spot sits
A close up of the facial markings would also help in the process of elimination.
I edited your pic to get a better look, so maybe it will help others with a better eye than I.

Awesome, thanks for responding Duane.

I have been looking into it myself but I keep finding conflicting information regarding the facial markings. Every time I think I've nailed it I read something contradictory.
The tear shape marking is long and thin, it lightens and darkens depending on either light level or mood.

This guy is very timid, if I approach the tank he shoots into the plants or driftwood. Very difficult to photograph.

I was thinking of getting a wild form blue acara (not a big fan of the electric blue) as a centerpiece single to go with my maculipinnis group. This guy came in with them as a contaminant. I've always loved the look of the adult diadema.

I managed to get some pics in natural light for the face markings, it really seems to accentuate iridescence.
sorry for the dubious quality.

Hopefully this helps!