If you are going to get serious about breeding I would remove the rocks on the botttom of the tank. It makes cleaning the tank SOOOO much easier!
How old are they?
who long have they been in the same tank?
What is the pH of the tank?
What is the Temperature of the tank?
What are you feeding them?
Nitrites, nitrates, amonia levels? (if you have a test kit)
What is the aquascaping like?
Are there teroccatta pots upsidedown?
Are there slates leaning up agianst the side of the tank?
Are there tank mates?