In my opinion, I would say that it is up to you which way you choose as far as grain size for your benthic area of the tank. I employ a deep sand bed for my reef tank with great success!
Oh, as for the grain size again, it would have to do with the types of living animals you wished to keep as many require various grain sizes. Ultimately diffusion and advection will show their ugly faces no matter what size sand grain you employ and detritus etc. will be draw into your sand bed. But their are ways or reducing this... Incorporate your live rock ontop of eggcrate with the sand underneath that. Also, an increased water flow to the bottom of your tank with efficient filtration will help as well as reduced feedings! _________ 125gal.w/Mag9.5 return(dual megaflow)>Mag7 pump Aqua Cev180skimmer.Wave2k Hamilton Reefstar(2)250watthqi(mh)pend.a Yellow, Naso Tang Red Lip Blenny Percula Clown Demoiselles Niger Trigger F. Wrasses Ceriantharia Orn.Shrimp and Stars Hermits Queen Conch asst. snails> Stars Zoos shrooms Montipora Brains Gorgonians Favia Turbinaria(large+small polyp) Acropora Xenia Tridacna (CroceaMaximaSquamosa) Leathers <35+75gal.reef tank as well> 
"IF THE PHONE DOESN'T RING...IT'S ME"  jb  |