Most catfish like to live in groups of 3 at the minimum. They're sociable, unlike our beloved bettas.
I just bought 4 Ocellifer Syndontis. I have the goal that they are going into the 29 gallon. (They're in QT now) They may get to big, but I chose them on the parameters of being able to withstand harder water & higher temps, and they eat a varied diet, but it does include more algae than most. Same with the Oto cat I bouhgt. Problem with them is they're tiny, practically invisible, and they'll never be big enough to make a dent in the 29 gal, so they're headed to my male's tank (divided 10). Add a buch of RCS & snails, & I hope this is the receipe to keep algae down (plus more real plants, of course). I don't kid myself that I won't be scraping algae of the tank walls, but it would be nice to have the leaves of the real plants tended to.
4 bettas: Butch, 3-year-old violet male PK EE & 3 girls in a 30 gal sorority. I do not name the girls anymore! 1/2 of them die within a month.
30 gal: 9 Oto cats, 4 Ocellifer cats. Inverts: Cherry shrimp & 2 assasin snails.
10 gal.: Butch, his 5 oto cats, 3 assasin snails, and a few snails the assassins haven't caught.