THE PET STORE ACTUALLY PUTS A KIND OF LIQUID ON THE BACK OF THE TANKS AND POURS THE CRUSHED CORAL ON IT WHEN IT DRIES IT STICKS TO THE BACK OF THE TANK AND BECOMES THE BACKING. THE GUY SPEAKS BROKEN ENGLISH AND THE BEST HE CAN CALL IT IS LIQUID FIBERGLASS WHICH I AM SURE IS NOT WHAT IT IS...