Some is collected  , some it farmed. It would be good to a visit a large successful salt shop. It takes the same conditions to keep corals healthy as to grow them, so these shops often grow some coral . I think it is acropha coral that is most easy to grow. Corals require a LOT of light. I suggest starting with easy fish ( damsels , wrasse, gobies  , etc) and inverts ( shrimp , crabs, starfish, etc.) to practice before trying corals. I had salt about 20 years, but now I go to a good shop if I want to see salt aquariums; much easier and cheaper than having one.

Some is collected, some is farmed. It would be good to a visit a large successful salt shop. It takes the same conditions to keep corals healthy as to grow them, so these shops often grow some corals. I think it is acropha coral that is most easy to grow. 

Corals require a LOT of light. I suggest starting with easy fish (damsels, wrasse, gobies, etc.) and inverts (shrimp, crabs, starfish, etc.) to practice before trying corals. 

I had salt aquarium about 20 years ago, but now I go to a good shop if I want to see salt aquariums; much easier and cheaper than having one.