No cichlid hard to breed - I can think of a few that are hard to keep alive, let alone breed, and not just on size grounds. Discus are prett straightforward. There are some geophagines from fast flowing water that are pretty tricky, and Teleocichla are very, very difficult, though some have now been spawned. They're about equivalent to spawning gold nugget plecs I would guess, and that's not very easy.