Janne, I think you're right [why wouldn't you be, you've bred more species of Loricariidae than I've ever seen (at least if we don't count photos as "seeing")!

]
I didn't think about doing a size-reference. The glowlight tetra is bigger than the questioned fish - and closer to the camera, so I guess the fish in question is about an 2-3cm long, which means that young P. maccus is a good match.
--
Mats