Introduction
Flocculation is a process in which tiny suspended particles in the pool water bond together into larger clusters, making them easier to filter out. Aluminum sulfate (often called alum) is a common and effective flocculant used in pool maintenance.

How Does It Work?

When alum is added to the water, it helps gather small particles (such as dirt, algae remnants, and oxidized matter) into larger “flocs.” These flocs float or sink more easily, allowing the filter system (sand or diatomaceous earth) to capture them effectively.

Key Points

• Some chlorine tablets also contain aluminum sulfate and cyanuric acid (CYA), offering both disinfection and flocculation.
• Liquid alum (e.g., “Alum 25”) is commonly dosed via a metering pump. Ensure there is at least a 10-second contact time before the water reaches the filter, allowing the flocculation process to begin.