I used blasting sand for my dsb, it's now 2 years old and I've been very happy with it. The silicon in the sand does not get absorbed by the water in the pH of a reef tank. My measured silicon levels are zero. I got it in the east bay so you may be able to find a closer place, but here's the details of where I got it.
Rental Service Corporation/Prime Equipment, 8001 Oakport St., Oakland 94621. I got 100 lb. bags of "Media, Lapis Lustre 60, 40x70. It cost $7.20 per 100 lb bag. Their phone # is 510 635-8485. They were a little surprised at the reason for my purchase, but very accomodating once they got past the unusualness of the request.
Here's a picture to give you an idea of the sand color.
Johara