I do the following:
10-15gallon tank, sand bottom, a piece of slate proped up against the side of the tank, to form a hiding spot.
add a heater, and a filter, air or box filter.
Then add the fish, feed as said above on frozen blood worm and high quality foods, mine do really well on king british catfish pellets.
Once the females look very plump, do a 50% water change with cold water.
This can trigger spawning, also stormy weather works well, so if its going to storm do you water change, this combines with high atmospheric pressure and again triggers spawning.
hope this helps.
Also are you sure they are C. julii?