Oh, and you do not need to swap it out for new. I reuse it and I am still on the same bag I bought 4 months ago! Even with a 75g tank, 2 10gallon tanks, and a 400g pond using it.
Best stuff in the world. I use the thin stuff rubberbanded around the intakes to my filters when I add new sand and I have clear water in 2 days! I do not even take the time to wash the sand, just use quilt batting and viola!