yes, your fish store is right.. you could probably have about 20 fish. but 20 fish that are SMALL when full grown. angelfish get very large, if you have small ones now, that means they're young (like babies) if they remain in a tank that is too small for them, they'll be very unhealthy. their growth will stunt, which means all of their insides are trying to grow, but their outsides wont let them.. think about if you were still the size of a baby, but your organs and bones were trying to be the size of an adult. it would put a LOT of strain on your body.i actually did talk to the fish store guys and they said that about 20 fish would be enough for a 36 gallon tank. and plus my angelfish are really small just like the rest of my other fish, becasue they r freashwater and i dont even have 20 fish in the tank.
This messes with a fish's immune system too.. its harder to keep them healthy, and they often will develop personality problems too (fighting with tank mates, or hiding out of sight)
i know they're pretty, but i would definitely take to angelfish back.. if it's not too late you may be able to get your money back. but even if you can't, they need to go back.
get the soap residue out of your tank
then read the link in the first post in this thread... its very informative.