I kept Florida Flagfish - at first 2 females and then 1 male and 1 female. They terrorized my Corys, ripped my Betta's fins to shreds, and eventually ended up back at the pet store (I also saw one of them make a snack of a red cherry shrimp). But, since they are technically shoaling fish, I think this behavior can be avoided if they are kept in larger groups of at least 5. Still, I was surprised because all info about this fish says that they are generally peaceful and only become territorial when breeding (which mine weren't).
On the bright side, they did eat thread algae, though I think they preferred Spirulina flake food more.
On the bright side, they did eat thread algae, though I think they preferred Spirulina flake food more.