Home Depot garden center. They have paver sand, pea gravel, river rocks, and pond rocks. I just bought another 5 bags $21 total. In my festae pair's tank, I used 1 bag of sand, 1 bag of pea gravel, and 1 bag of pond rocks. They love it. Just be sure to rinse all of them until the water runs clear. There's a lot of dust that will milk up your water. I've been using these in my 210 for several months now with no problems.