The common rule of thumb with angels is start with 6 and wait for a pair to form. Once there is a pair remove the other four by giving them a separate tank or rehome because the pair will cease to tolerate others especially when spawning. The easiest way to sex them is after a pair has formed and then getting to observe the spawning process.
You can try adding a single specimen but the original inhabitant may not tolerate a new comer. I prefer wild types but you can add any strain that suits your fancy. The full black seem to be more aggressive imo.
You can try adding a single specimen but the original inhabitant may not tolerate a new comer. I prefer wild types but you can add any strain that suits your fancy. The full black seem to be more aggressive imo.

