Ya, as long as you don't mind losing any life that may be in it, go for it.
Something you may try would be to keep the sand where it's at, make some rock, cure it for a month, take it out and let it dry fully, then bury the rock in the LS for a week or two, then put it in the tank you want. It will kick start the growth and pulls the "good stuff" in when it absorbs water.
Yes, white portland cement. It's $13-18 per bag, but that's what it has to be. One bag will make you a lot of rock.