Alternate substrates

I'm sure not everyone here is running bare bottom or running argonite sand. Can some other folks tell me what they're using. I am asking because I found very inexpensive crushed limestone sand (argonite is a type of limestone). It gives the good ole fizz with vinegar so I know i'm in the neighborhood, I think this is simiilar to the southdown sand that was impossible to find but a blessing if you did find it.

Any other ideas,and any ideas if what I found is safe?