Check the listing for details. BioGuard Back Up 2-1 Quart, Pack of 2, Proven Effective Algae Preventative. Condition: New. Listed at 57.98 USD. Highly Effective Algae Preventative: Our non-staining highly effective formula prevents a wide variety of algae growth. Weekly use of Back Up 2 prevents before it starts. It's stable in sunlight and will not evaporate. The activity of this product increases as water temperature rises, which is when you need protection the most. Powerful Wetting Agent: Our Back Up 2 has a powerful surfactant agent, which makes it able to work in the tiny cracks and crevices where algae starts. It does not affect pH levels. Direct to Pool Application: Add this product directly to the pool by pouring around the outside perimeter of the pool while filter and pump are in operation. This product is not recommended for use in pools that feature attached spas or intricate water features. Compatible with the 3-Step BioGuard Care System: This product seamlessly integrates with either the 3-Step or Once-A-Week 3-Step BioGuard Care System, offering flexibility and convenience for pool owners. The addition of algicide is needed for proper pool maintenance. Tested and Proven Effective: BioGuard products are known for delivering reliable results and making pool care easy. BioGuard carries an extensive line of pool solutions for all needs.