Jim's right; make sure you smell the sand before putting it back in. Actually, you should smell it as you're putting it in the storage container and just throw out (or wash and dry) any rotten egg smelling sand right away. If you have a 3-4" sand bed, you probably have a couple hundred pounds of sand at least. If a fairly large portion of it, say 75 lbs, is good but the rest is bad, that's still a great amount to seed a new sand bed with.