I keep wild altums. They are one of the most difficult fish to keep alive and even harder to spawn. After several failures, I finally learned how to keep them alive. The ones that lasted when they arrived they went into a tank with a pH of 4.2 and it took me six months to bring them up to when I now keep them, at 6.0. I use an ro/di unit and have a continuous monitor for pH, TDS and temp. on the tank.
I normally do not like to send members to other sites, but in this case it is important, There is an amazing site dedicated to wild angels and it includes info on domestics as well. It is where I learned how to keep altums. This site is unusual as you can only read the forums there if you are a member, Normally this puts me off of any site and I refuse to join if I cannot look first. I made an exception for this site. However, there is more to the site than forums.
http://www.finarama.com/
If you are really interested in altums, there are two great vids on them both in the wild and then being sent to Simon Ferkel in Germany who is one of the very few people in the world who does so, Watch them in order:
Many angels in the wild tend to live within larger groups of discus. In a group of discus there is a perimeter guard of the fiercer larger discus who act to protect the group. The angels take advantage of this. There are no discus where altums are found. Have a read here
https://www.practicalfishkeeping.co.uk/features/do-angels-and-discus-live-together-in-the-wild/