All depends on what type of LR you are buying - cured or uncured. I definitely wouldn't try to cure uncured rock with sand in the tank since you're tank is going to be 1 smelly mess for a bit. If it's cured rock, the die off shouldn't be bad & you could do it with the sand in there. Be sure to put the rock in first & back fill with the sand. That way it'll be on a stable base. Should you get burrowing fish in the future their digging won't cause the rock to come tumbling down. If you want some substrate with critters, check out GARF's Grunge - it's full of stuff. Don't use it as your top layer though since some of the rubble in there can be on the dark side. GARF's site is
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