With the hand of luck, i would say add another female or two in the tank. They might not be compatible at all. Even if you bought them as a pair, there still might be a chance they might not pair up. The biggest change would be environment. Same thing goes for betta's, if the female isn't interested sometimes the male still make a bubble nest. He's ready to breed, but not necessarily with that female. Sometimes forcing two fish to pair up might end with one killing the other. I suggest adding more females to the tank.