Hi, I just bought Target brand Play Sand from Home Depot. It says it's safe for sand boxes, playgrounds, icy driveways, and gardening, and it's been pre-washed and sanitized. But when I started dumping it in the tank, big clouds of dust (I think it was dust) came out of the tank and it made the glass tank walls a bit dirty. I think it clumps a little bit when wet, but my crabs seem to be okay with it and one has burrowed in it. Do you think it is safe for them? Is it normal to see that cloud when you first dump it in?