Natural Chemistry extra strength stain free is an all natural stain remover This Natural Chemistry extra strength stain free is an all natural stain remover. Recommended dose is 1-pound per 10,000-gallons of water. It can applied by following way that balance pool water and lower chlorine level to at least 1 ppm. Then add stain free as per dosage around the perimeter of the pool with the pump running. Brush pool thoroughly. After brushing, if stains are not completely removed add more strain free extra strength. Add a pulp based filter aid to your cartridge or sand filter. If you have a DE filter, make sure it is properly charged. Add metal free at a rate of 33.9-ounce per 20,000-gallons of water. Vacuum pool slowly and thoroughly.