Ted's observed that we often keep pelvicachromis in pairs, but that the presence of additional females is important to encourage spawning. So, especially for some of the more aggressive (or expensive) Pelvicachromis, putting a mirror in the tank for a short time can trick the female into thinking that there's competition around. She'll put on her aggressive/spawning colors within minutes to show off to the other female, and this then gets the male interested as well. After a bit, the male and female start interacting and ignoring the mirror. That's when you take the mirror out and hope they spawn. In some cases, he's had spawning happen within minutes of putting the mirror in the tank.