Additional Details ------------------------------ Directions: This product is a 100% calcium carbonate filter media for pH correction, also known as calcite. It prevents blue/green stains and corrosion of copper plumbing in water with acidic levels. can be used upflow or downflow (backwashing) tanks. A gravel support bed recommended. The range should 5.0-7.0, depth 24-30 inches freeboard 50% (minimum). backwash rate 8-12 gallons per minute square foot, the expansion 35% depth. service flow 3-6 but may modified to adapt local conditions.