Applied Biochemists Staintrine is a dual-action formula that combines a stain-remover with a sequestering agent to quickly remove even the most stubborn stains. Its professional strength, easy-to-use formula can be applied without draining your pool and swimming can resume immediately after treatment. No testing is required with this product. Simply treat your pool and follow with weekly doses of Applied Biochemists Resit to prevent future staining. Best of all, Staintrine is made by Applied Biochemists, a leader in bio-based pool chemicals, allowing you to buy with confidence.