Angelfish not eating

Question
Hi.  I have a 46 gallon bow front tank that's been set up for approx. 3 months.  I have 4 angels, two that are quarter sized and two that are about the size of a coke can diameter, if that makes sense.  It's the two larger angels that I have a question about.  I'm not sure what kind of angels they are - they are silvery colored with black stripes and yellow coloring on top of body.  I feed them a diet of mostly frozen baby brine shrimp, and every once in a while flakes.  3 days ago, they suddenly stopped eating and are just staying in one spot of the tank together.  I don't know a lot about fish disease, but they do not appear sick, their breathing is fine, I don't see any "ichyness" on their bodies.  
I test my water once a week and do weekly water changes.  My tests always show great water quality.  I have a power filter and one air stone in a planted tank.  
I also have 2 small bala sharks and 3 otos.  
Why won't my angels eat?  Are they sick?  
Thank you!

Answer
Hi Dawn,
Since they are staying together, and have no signs of illness on their body, you must have a couple.  Watch them closely, they should soon do the "Nuptial Dance."  This dance is to make sure they are of equal force. (They grab each other my the mouth, and pull waltzing all over the aquarium,  stop, go back, and do it again several times.)  If they are not of equal force, the stronger one will pick on the weaker one, sometimes causing death.  If they are, you have a couple getting ready to spawn, or they have spawned, and eaten all the eggs!   You may have missed the Nuptial Dance!
Once you have a couple, they will defend their eggs.  Angels are tricky...sometimes both fish care for the young, sometimes only one of them does,  and sometimes both eat the eggs, and blame the other one...lol  It's lot of observation.  If you do have a couple, you would be better off giving them a tank of their own.  Breeding Angels is easy once you know who cares for the young which may take a few apawns before you get it right.  
I also would like to add, that feeding them dry or frozen bloodworms should also be part of their diet, as well as daphnia.  The more you vary their diet, the healthier your fish will be.
I hope this helps.
Lynda