You don't have to use ARM media. If you can find any crushed coral about the same size that will work as well. I was having a tough time finding a source though. I don't think there has been much of a demand for large grade crushed coral as a substrate since the early saltwater days.
I ordered mine from Premium Aquatics, next day delivery and they're a big supporter of SLASH
I ordered mine from Premium Aquatics, next day delivery and they're a big supporter of SLASH