Sounds like they have picked thier spawning area, if the female hangs inside the cave while the male guards it. Could already be eggs in it, or they could be getting ready to spawn. I have almost 2 week old FireMouth fry in my 20g, and my FireMouths are already doing the spawning dance. So once you get the water parameters just right your fish will spawn all the time especially with convicts since they are the rabbit of the cichlid world. They spawn like crazy. My pair of Cons is getting around the size to start spawning soon. They have taken over the cave in the tank. I'll be getting a huge 100g or larger for the rest of the fish in my 29g tank with the cons.