Corydoras Changing Behavior

[MapleNeil]

Hi,
I've had these 6 corydoras for at least a month, they root around in the sand all day usually.
A few days ago I made two changes. I changed the direction of the flow from the two TopFin 20 submersible filters, and I added two Golden wonder Killifish (striped panchax). The reason I changed the flow was to avoid having strong current at the top where the new fish would live.
Since then, the cories all just sit on top of a big rock most of the day. The killifish like the bottom feeder pellets I drop in for the corydoras. But if they were afraid of the killifish, I don't think they would sit on top of a rock, making them more exposed. Is it possible the killifish scared them away from eating their pellets? Or more likely the changed flow has made it hard for them to be down on the sand? or something else?

 

[Aiken Drum]

Corys are nocturnal feeders. Maybe without other fish they where less cautious and fed during the day, but the new fish has triggered more natural behaviour. Not something I've ever seen with my corys though. They always feed whenever i put in food.

 

[MapleNeil]

*sigh* I think I figured out what was wrong the the cory's, I added an apistogramma, and while he seemed quite peaceful, he must have been harassing the corydoras. That would explain why they were up on the rock. But I don't understand why they won't eat. I've put them in another tank and they are doing very badly and not eating. Also I moved things around in the aquarium and raked the gravel and ammonia levels went up to almost 0.5 for a day or so. Now the water parameters are good again but the cory's aren't going to make it I'm afraid. I just wish i knew whether the problem was the ammonio or the apistogramma.