Make sure the water is soft. When you do a water change, use 20-50% tap water (depending on how hard it is) and the rest RO.
Feed them mysis or blackworms to fatten them up. I prefer frozen mysis.
Put in plenty of flower pot caves, make sure they don't face each other, so the male can hide out of sight from the yellow female, who gets mean when she has a cloud of fry.
Also, something I've found is that Apistos will breed better if slightly crowded. If you only have one pair, I'd put them in a 10 gallon or 20 long. I've found that 1 or 2 pairs in a tank that size do not breed as well. For a tank that size, I'd recommend having 8-10 apistos (I'm assuming a 4' by 1' footprint, is that right?) A lone pair in a big tank would never breed for me when I was into it, but moving them to a smaller tank helped.