I use black Diamond sandblasting sand in my reef tanks. It's inert so doesn't leech calcium like aragonite sand, but your live rock does that anyway. It's 8$ a 50lb bag most places, took 2.5 bags to give my 125G a 4" sand bed. You can but it at Tractor Supply Company. Try to get Fine, medium or coarse grain size, the extra fine will blow around with powerheads. It's a beautiful black sand that won't leech anything at all into water, including silicates as it's processed coal slag. It must house bacteria pretty good as well as I have a sand sifter star in the tank going strong after months, just saw him last night after not seeing him for weeks. The only real drawback is the same one you'll have with any black sand, you'll need a little more light than you would with white/beige sand.