I am keeping angelfish (Pterophyllum scalare) for couple years. In 30 gallon tank I had one couple and a female separated by glasswall. They hate each other. The male from breeding couple died some time ago. After a 40 days I took glasswall out. Both females were very friendly and recently they give me eggs and fry. I know reef scool fish could change sex back and forward, I also have seen swardtailes could do it, but nothing I could find for Pterophyllum scalare.
PLease if anybody have same expirience just drop me a word!