Greetings danielle_adam,
There are several ways to determine the sex of angelfish. Two of the methods I find helpful are:
-Letting several of them pair off on their own. (Easier and more reliable.)
- Observing their mating tubes, located between the ventral fins and anal fin in the vent area. The females tube is more pronounced and somewhat larger than the males, the males tube is shorter and more defined.
I hope this helps.
Cheers!
Raithan O. Ellis