BioGuard SoftSwim Stain Control helps prevent metals from settling in the water and staining pool surfaces. This product is intended for use in pools with plaster surfaces, or on any surface where dissolved metals such as iron, copper and manganese are present. Stain Control also helps maintain the presence of SoftSwim B and C. Each SoftSwim product is formulated to work specifically with the biguanide chemistry of the SoftSwim program.