Corydoras and synodontis euptera?

[AteItOffTheFloor]

Have a chance at a fish pond. Its 6 long, 3 feet wide and 1 foot deep.

Have filled it with sand and plants. Now considering stocklist.

Really want to get a school of corydoras. About 20 of them swimming together would look awesome from the top.

But I also want a pair of jewel cichlids, to see breeding and brood caring. However, I do not want to be overrun with fry.

So I need to get a fish that can reliably eat the eggs/fry, or at least most of them. My immediate thought was a featherfin syno. But my concern would be whether it would outcompete the cories during feeding time, even in a pond.

I also plan on getting a rainbow shark/rtbs. Does anyone know if this guy is a nocturnal hunter? If so, I could do away with the syno.