How large are the Mascara barbs? Mine are around four inches and I have some Sumo loaches (2.5") with them and the loaches are fine. The sumo are very active and dark in and out of the rocks piles I have set up for them. They chase each other at times and at other times them sit together, depending on their mood. Another fish I just love, though not a loach, is panda garra. I have six and they are a hoot! They act very much like loaches in the way they hang out together. Sometimes all six will lay in a pile or work their way over the rocks grazing as they go. Sometimes they squabble (I saw two fighting for half an hour once), bashing their heads into each other, yet they never damage each other. They just don`t have a mouth that would allow it if they wanted too.