Check your local big box hardware store (Lowes) for a deal on DE. I just happened to walk by a big rolling cart with a sign that said 75% off. There was a sampling of old, dusty pool and spa chemical treatments -- not interested, and then I spotted these big crumpled, not quite new-looking boxes on the bottom. It said DE for DE Filters and contained 25 lbs. There had to be 8 or 10 boxes. I got one for $2.71. Should last me a good long time.

As long as I keep it dry, it should be fine, right?