I just don't buy the theory that silica based sand has anything to do with diatoms. Many people use it in tanks, sand filters, DSB's and remote or bucket DSB's with no diatom growth. I used play sand in my tank when it was fish only and I didn't "know better" and there is still some in it with not a single bit of diatoms seen in the better part of a decade. In fact diatoms are probably the only nuisance algae this tank hasn't had at one time or another! There may be more functional choices, but if your mainly concerned about looks then silica sand should be OK.
I would add though, if you are vacuming it to keep it clean (good idea) then you would probably be better off with a much shallower bed, say 1-2" max. Most sand stirring critters wont go deeper then that and your chances of buildup and a resulting crash will go way down. I had a 4-5 inch bed of mixed aragonite and sand of different sizes and I found not vacuming only worked for a couple of years, and then siphoning was only partially effective because you can't get under the rock work etc. I ended up pulling 2/3 out last year which was much better. I just pulled out 99% of the rest to see if I can live with a BB, but I am probably going to add something shallow and more uniform back when I move the tank in late august.
If you have a nitrate problem use a remote DSB or DSB bucket. They are cheap, effective, easy to clean or change out every couple years if necessary, and way less of a crash risk then an in display DSB. All you need is a container of sand (fine aragonite prefered), water flow from a pump or gravity, and perhaps a bulkhead or two.
. A deep bed of crushed coral won't create anaerobic aereas within it which is where some poison producing bacteria can take root. Because it lacks these anaerobic zones, there's no need to worry about disturbing it and you should do whatever you can to vaccum as efficiently as possible 
