Well it's like this:
Saltwater and freshwater are two completely different animals. What you have is referred to in the hobby as "crushed coral" which can also include shells.
The majority of us use animals (what is referred to as a "clean up crew") to keep our sandbeds clean. If you want to do the extra maintenance and keep things vacuumed on a weekly basis, have at it. But down the road when you have nitrate problems the first thing we're going to suggest to you is swapping out your substrate. Not that you would listen. Since you have ALL the experience you need.