I've got a 5 gallon tank that is home to a male Betta (mellow personality,) and 2 days ago I added 3 glass catfish. I got the glass catfish specifically because they are reported to be reasonable tank-mates for less-aggressive Bettas, and so far it has worked fine.
The glass catfish seem to prefer the bottom corner opposite the pump outlet, that the pump outlet is pointed at; they just school within that current. They rarely move towards the surface of the water, even at feeding time. If a piece of food sinks and then drifts in their direction, they'll ignore it unless it practically hits them in the face. Then they'll lunge and swallow it faster than you can blink. This differs from behavior I've seen in Youtube videos, where they'll swim up for the food.
Presently, I'm feeding them fish-derived flakes, because I didn't know any better at the time. I intend to buy some frozen worms tomorrow, but I've read that flakes are at least OK for an occasional meal.
I'd like to know what, if anything, I can do to encourage them to get up to the top of the tank before Betty[*] eats all their food. I could possibly redirect the pump outlet to point closer to the surface of the water, but that will make the Betta's food sink faster.
[*] Child insisted we name him Betty... can't be helped.