It's generally impossible to tell male from female. The only way we could tell for sure was to watch which ones laid the eggs, and which ones did the fertilization. They paired off on their own, and prepared their own laying sites (often a swordplant leaf, seldom hard surfaces). Both sexes share equally in ALL aspects of the whole ordeal, all the way through to protecting and rearing the young swarm. After couple of years of it, we gave up breeding angels cuz they were too prolific (too many babies) and they killed off everything else in the tanks (125gal) to protect their young. They get VERY aggressive. Your 3rd angel is gonna die. Your bala might too. Your pleco is safe (if quiet).
Newbie parents often eat their eggs. Angels lay eggs about every 2 weeks. Some pairs developed a taste for them (some eating while laying). Fewer pairs were good enough to raise a whole swarm of fry. A swarm is so cute. Mom & dad try so hard to contain the swarm, but are not so good at shepherding. The fry are tiny (2 mm) so can get sucked into filters, etc. Takes 2 months to grow to 1 cm body diameter.
To get the highest yield, I often removed the eggs into a separate hatchery tank (a floating jug is OK), aerated them, cleaned them (eye-dropper) 4x daily, and fed them 2x daily. Raising brine shrimp was the best food for fry. You can get about 400 fry per batch, but only about 50 survive to adult, if you're REALLY diligent about cleaning. Good parents get about twice that yield.
But even good parents will eat the little ones in a few weeks (as intruders), when the next batch is laid. So you'll need to remove the free-swimming babies eventually.
A clear-glass turkey baster is handy. It's a small chore, but raising babies was rewarding.
This was a good web site:
http://www.geocities.com/fgrainer/rasisingangelfish.html
