The Natural Hot Tub Company Penetrating Spa Cleanser 16 Ounce Bottle Works to clean away chemical residues and contaminates which have built up deep inside your spas plumbing, fittings, and equipment. Use once a year to deep clean away built up contaminants that reduce your spa and equipment's life expectancy. Works by cleaning away current chemical buildup and helps prevent future build up. Not necessary for new spas, but highly recommended for first time users of our products. Each 16oz bottle treats a spa up to 500 gallons.