A large water change together with moving some pots around always seem to get my convicts in the mood. Other times, I will remove the female for a couple of days in another tank and return her and that seems to get them going as well. Honestly, it's so freakishly easy in my experience that I'm surprised yours haven't started. I'm sure it'll happen soon, then you'll be looking for an Oscar to help with the hundreds of fry you'll be wondering what to do about.