Large- and not shy. Thats about my only 2 requirments. I've got lots of
different types of plecos, they are one of my big 'things'. I keep a 16"
sailfin with my arro, no probs at all. The big guy holds his own very well.
An arro will pick on any new arrival in the tank, regardless of size, until
they at least figure out what they can get away with. A smaller fish, even
a pleco will be hunted even if they aren't likely to be eaten. A big one
is going to make its prescence known in a hurry. Arro are smart, they
figure things out pretty fast. If its shy, it will stress out, even if the
arro doesnt eat it because he will still peck at it. I would put a large
pleco in with a flowerhorn as well, but no way would I try it with a
small one. Even if they cant eat it, some fish just like the hunt/kill part-
arros do as well, to some extent.