If you are wanting a sand sifting animal, I dont think you want crushed coral. It tends to be sharp and can cut from what I understand.
I have three different substrates in my tanks. I have two bare bottom, two with Carib Sea Super Reef Aragonite Sand, which is coarser, and one with a CaribSea Aragamax Oolitic Select (fine) Sand. The two with the coarser reef sand, one is very shallow, less than 1", and the other is 2-3" deep. The tank with oolite (fine) sand is 2-3" deep. The reef sand, I rinsed in rodi water three times till the water just barely turned cloudy before putting it in my tank. The fine sand came with a packet that helped clear up the cloudy particulates in a day or two. I think that if I had to choose one over the other, I think I would also go with the fine sand. I like the reef aragonite, which is a little coarser sand, for my sand sifting goby. I think for the sand sifting starfish, I like the fine sand better. Also for the clams, I like the fine sand better. They may like it better too. As far as looks...I think I like the fine sand better. The shallow reef sand bed is easier to siphon detritus out of though. And the bare bottom is even easier. It is really a personal preference as to what kind of animals you want to keep and what you like for looks as to what type of substrate you want to use.
