Agree, this would be the #1 defining factor in what all OP could "potentially" add in as a tank mates of sorts. If it's on the small end like a 55g I would recommend either a striped rapheal catfish or some nerite snails, or if it's on the larger end like a 200g I would then recommend either a school of mascara Barb's or maybe even a couple more cichlids such as a convict or a salvinni. Also another option, if your not against occasionally buying more fish, you could add in a big school of zebra fabio's, just know that they will slowly get eaten up so you would need to occasionally buy more.
Yeah sadly that's the case with most FH's. That's why I would mainly go with species that are either fast enough to escape or tough enough to handle the abuse. Also I find that having something that's nocturnal can also work just due to both fish being active during different times.
