I was unable to find the fantasy sand at my local HD, but they did have something called "High Desert" play sand, and I got a little sample from a ripped bag. It is pure white, graded, fairly fine grained (but not as fine as your typical marine sand), and has a somewhat rough texture (like aragonite sand...it has that irregularly shaped grain with a shiny side). But the good news is, it fizzles like alka seltzer in vinegar. I put it in 20 minutes ago, and I think some of the smaller particles are visibly dissolving now. It does have a warning on the bag that it contains "small amounts" of silica, whatever that means, but it appears to be mainly carbonate based.
Does this sound like a decent sand for a reef? I may pick up a few bags of it. It does seem a little rough for burrowers (not like the soft, powdery marine sands), but I don't have (or plan to have) any sand sifting fish (just nassarius snails and the various pods
and worms common in sand beds).