I've been using sand in my water pan since sometime last year. I cover it with HD foil, and Sunday, while I was throwing out the foil that was covering it for the smoke, and replacing it with new, I noticed that the sand was a little hard in places. I've been just leaving the same sand in the pan, and re-covering it each time. What do others here do? Do you use new sand each time, or just keep the sand in the water pan?