It is quite normal for them to be preoccupied, and it's even better not to feed them right away with new eggs. That's just my experience though. I've had my keyhole cichlids start fighting very seriously after a feeding. Don't know why though, but it was right after they were done. Maybe because noone was watching the eggs for a while?
There are anti-fungal products out there, but I don't know if it's ok to threat the whole tank with that stuff. You should read the instructions on the package for that. Or let someone else answer that question here