Do not buy an adult pair of angels if you want to add small fish like tetras. If you want a single pr of angels in the tank and nothing else, then buy the adult pr. But if you want a community tank then buy young angelfish and grow them up with the tetras and other fishes. Big angelfish will eat small fish that get put in the tank with them. If you put the adult angels in the tank then add tetras they will say "mmm food".
In addition to the big angels eating things, you don't know how old they are or what conditions they were grown up in. They could be 10 yrs old and die next month from old age, or freak out because they were raised in soft acid water and your water has a different chemistry. Young fish are more adaptable and they are young so you have a chance to keep them a lot longer. Buy young fishes and grow them up together for a happy community.
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Angelfish have been bred in captivity for 50years, as have most common freshwater aquarium fish. Unless you specifically buy "wild caught fish", any freshwater angelfish you buy will be captive bred and will be able to tolerate a wider range of conditions compared to its wild ancestors. And wild caught angels are expensive and are sold as specific species.
eg: Wild Angelfish Pterophyllum altum (Orinoco). They will have "wild" the species "P. altum" or "P. scalare", and river system "Orinoco" they come from.
Wild angelfish will also be the classic silver and black stripes. You won't get gold, marble, black or any fancy colours or fin shapes.
As long as your water is not extreme (pH 9.0 and GH 500ppm), domestic angelfish will be fine. 20yrs ago I regularly bred angelfish (and other soft-water fishes) in water with a pH of 8.5 and GH of 350ppm. The fish I used for breeding were bought from a local petshop and originated in Asia just like millions of others that come into the country every year.
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off topic.
I too learned (I think from the BBC Planet Earth series [1 or 2]) that entire coral reefs are dying from a presumed increase in water temperature (although I thought I heard 2 deg C). It seems almost inconceivable that numerous species in a coral reef would be so fragile as to die off from such a slight change in temperature. I have to wonder if other forces are/were also involved?
Coral bleaching is caused when stressed corals are pushed past their natural limits for temperature. There are corals reefs that are unpolluted and their temperature gets just as high, even higher than other areas that bleach. And the unpolluted coral reefs do not bleach. Pollution, mainly nutrient run off, stresses the corals and when the temperatures rise, they can't cope and expel the zooxanthellae (algae in their cells) and bleach.
Fortunately coral larvae that settles in deeper water does not get as warm and is less prone to bleaching. And corals can catch new zooxanthellae and survive.
They have also found a few species of coral that naturally occur on the Great Barrier Reef growing along the south east coast of Australia near Tasmania. The currents are taking warm water further south and some coral larvae are setting up shop in the cooler areas further south.
There is hope that corals will simply move into cooler areas and start new reefs. And the corals from unpolluted reefs will be able to repopulate areas around the world with their larvae travelling in the currents. Having said all that, people need to stop screwing up the planet.
