That is what I will most likely do -- keep a close eye on him.
When I purchase another tank, I will probably keep the Ctenopoma and a few catfish by themselves.
If I put feeder minnows in the 50 gallon tank, would that help deter the Ctenopoma from eating the larger tetras, or are fish more indiscriminate in their selection of food? I mean, do they see the smaller fish as an easier target, or will they just go after anything?