Use to fill in cracks between rocks to prevent water from being “lost” over the waterfall Improves water flow visually and black color hides foam in the shadows of the rocks Hand foam cans have a patented trigger system which allows multiple uses Can be reused for up to two to three weeks. Trigger will dispense foam in any position Fish safe, non-toxic formula BWFN is minimal expanding foam – fills in cracks with less trimming of excess foam