As you indicate; to combine Corydoras with Apistos usually is a bad idea. The Apistos will defend their territory, trying to chase the Cory's away.The latter don't understand their behavior, and keep coming back, again and again. At last, the Apisto will try to attack the only and most vulnerable part of the "armored" Corys; their eyes. Corys without eyes is not nice to look at.
So both species are stressed most of the time, and the Corys sometimes badly hurt.
Corys also sometimes eat small Apisto fry.
You could always find people saying that this combination works fine in their tank, but bad things happened so often that I NEVER recommend the combination.
In the nature, I've never found Corys and Apistos living together. Sometimes they, of course, are trapped in the same rest water pool during the dry season, but that doesn't mean they live together usually. Corys usually are found in the big rivers, while Apistos live in the forest creeks. I've found Corys of the long-nose types in the same small forest creeks as Apistos; no-shoaling species like C.fowleri and C. semiaquilus. These Corys are territorial, and live at least 1meter apart from each other most of the time. But I found them almost 100 meters away from the nearest Apisto.
I've tried dwarf-Corys like C.pygmaeus together with Apistos. That works much better, the Corys are not hurt. But they are not happy; they usually are chased away from all the hiding places, and end up lying all together in the open. They don't breed, and don't look happy.
The L-numbers catfish are usually most active during the night. At that time the Apistos rest/sleep on the ground. I've seen catfish, like Ancistrus and others, during the night, chasing the Apistos up from the ground and up among plant leaves in the top of the tank, again and again and again. After some time, the Apistos are stressed so often that they could die. In the nature they could move to another part of the river; in a tank they cannot move far enough away.
I've seen catfish eat Apisto eggs, and also make so much hustle and bustle in the tank that the Apistos loose or give up their fry.
Well, now you understand why I usually don't give advices of community tanks. I like the Apistos to have a nice time, to have the same surroundings as they have in the nature, and to show all their nice colors and interesting behavior. They usually have the ground for them selves in the nature, and I think they should in our tanks too 🙂
😀
