If you've already got a male, is there any way you can capture them both for belly pictures. It's a little harder for me to determine on the brown ones since their bellies are so dark compared to the light colored ones. But at that size, the new one, if I can see the comparison to the male I'll should be able to tell you what it is. It's very obvious in an L144 or an albino ancistrus at this size. Doesn't have to be today, just asking if you get an opportunity. Or you see the male against the glass snap his belly for me so I can put them side by side. I'll use the one from the new fish that you already provided. I'm still leaning toward young male.