I just wanted to echo, and push the water changes water changes water changes. Its usually not after just 1 water change that they spawn, but rather continuous weekly or twice weekly changes. Regular water maintenence with any fish is key for health and conditioning.
Spawning JDs, takes conditioning most of the time. Its very rare to find two fish, throw them together and have them go at it. My advice would be to find two specimens that co-habitate together, and spend a month or two feeding them everytime they are hungry. Whether its 5 feedings a day or 10...if they look hungry and are begging for food, feed them. They need plenty of nutrients to build up a healthy stock of eggs. And they will need plenty of water changes to keep the water pristine and to get them in the mood.
IMO, 3 things are really important for getting frequent and successful spawns:
Correct temperatures
Heavy feeding
Frequent water changes
You can't go wrong with that. :thumb:
Cole~