I have had a couple of pairs that bred consistantly but they were pretty much acquired by accident, The first time was in a 55g community tank that I had put 3 ABF in, one was a female and it paired off with one male which started bullying the other until I gave the outcast away, the second pair turned out to be a male/female and were in a 35g community tank. Both tanks contained heavy growths of elodea and a few open water patches. The butterflys like laying up on the plants. The water temp. in both tanks was 80-82 degrees F. and the ph was 6.6-6.8 like for neons. the water was also fairly soft, Dh 6. I never saw them mate and tended to not know that they had bred until I saw 1/4" ABFs swimming around, I would transfer them to a 3 1/2 g flat bowl until they were about 3/4" long then give them or trade them away.
Other than the water and plants I think that the key was feeding them. Because of the plants I could drop small earthworms in the tank on the plants and the butterflies would get them, I also had a nice population of scuds in both tanks that they munched on, mainly they got gut loaded crickets and earwigs, but they also got live brine shrimp and guppies, gambusia, top killies, and glass shrimp as well as the occassional tetra. The little ones got pinhead crickets, mosquito larvae, brineshrimp, and baby guppys.
The other thing I noticed is that the young would often show up a week or so after I had reves a gallon or two worth of plants and then replaced the volume with water, I noticed that the new water was usually a little cooler and slightly more acid than the tank water so I think it might have mimic the onset of the rainy season.
Both pairs were producing young 3-4 times a year.
They need meaty, live food to be at their best and if fed well they should go from 1 1/2" to 5 1/2" in about a year. The longest I ever had individuals was around 4 years and they were still breeding strong when I sold them before moving, I would not keep them in anything smaller than a pair in a 20g but you could keep one in a 10g I suppose.