Well. When I increased my barbs to 12... I had quite a few very small ones. After a few days the numbers thinned by 2... I thought they must have died and been eaten (as they were the smallest in the tank).
Cleaned out filter after after 2 weeks... jumped when a body bobbed up. Put fingers in and it went away... thought it just sank. As I emptied some water out, to my amazement was one of the barbs swimming around.
He must of been small enough to fit through the hole in the 3d background and got sucked up the filter.
Sadly I also found the 2nd missing one already dead in the filter.