Additionally, it takes a good quality angel to make for a successful specimen. Most of what they sell at pet stores are so terribly inbred that they are anything but hardy. And also often sadly lacking in parental instincts should they breed.
Try to get the closest to the wild type (or if you want to shell out the money - the wild type) as you can. Usually they are labeled as "silver" angels. The more red in their eyes, the better. I went through dozens of junk angels until I bought the current pair of silver almost wild types who have been showing good health. Also, adults will do better than juveniles.