Sand... I did not know that.
You can buy something called a cloneator or make one yourself
It consists of a large plastic box, (one the light can't come through)
a sheet of fiber board, (water proofed with paint, I used white) with
2" holes cut in it, ( mine has 48 ) some 1/2" PVC pipe, 1/2" elbows, 4
spinning sprinkler heads, and a submersible pump. oH, and some 2" rubber
discs to fit in the holes. I can get you a picture if you like.