what's the water temp?
i find that if the water introduced in a wc is slightly cooler they tend to spawn..but it doesn't always help. do you have a male and female(sometime difficult to tell on bolivians)
also you need to increase protein..I use bloodworms, brine shrim , mysis to help..they need the extra protein(conditions the fish)
generally they will spawn when ready..
lucky me..I have two spawning pairs..currently have to spawns in the tank..my pH is neutral I actually think that the water supply changes from summer to winter. probably addiditves to compensate during summer..all summer I didn't get successful spawns allthe fry diedand parent ate them..now it's cooler and the spawn are lasting..I have freeswimmers.first time since last spring.
are your pair even attempting to spawn? or are they spawning and the eggs aren;t hatching?