Changing out Sand. Good idea or not ..

[Faithinc]

For my 55g, I've gone with a mix of 50lbs of the first Caribsea mix you posted, with an additional 20lbs of fine sand. The fine will eventually sift to the bottom, allowing good sand-bed growth (worms and w/e you're looking for if your into sand beds) while the top shale-shaped sand has kept my bottom from turning up a dust storm every time my power heads + return are going.

I don't know if this substrate would be good for pistol shrimp. As i've read: Pistol shrimp will dig into rock if they don't have a solid packed substrate they can play around in. If you really want one of these little guys, I'd buy a really porous rock and bury it under your stand with just the top sticking out. At least then he'd have something solid to dig into.

But I'm just a noob and wikipedia is my friend.