1. Look, smell, and document
From the deck, note whether the water is green, cloudy, foamy, or has surface mats. Photograph the water and equipment without opening anything. A sudden change after heavy rain, heat, a power outage, or a chemical addition is useful context.
2. Confirm circulation safely
Check the controller display and listen from a safe distance for normal pump operation. If the pump is silent, the breaker trips, or you see leaks or damaged equipment, use the pump safety checklist and call a technician.
3. Test before treating
Use a current test kit exactly as its instructions describe and record free chlorine, pH, and any other values your product label requires. CDC identifies chlorine or bromine and pH as the first defense against swimming-related illness and recommends following the manufacturer's instructions for the product in use.
4. Keep chemicals separate
Do not combine products, pour one chemical into another container, or add chemicals based on color alone. CDC says never to mix chlorine products with acid or different pool chemicals, and to follow the label for any pre-dissolving. Store products in their original labeled containers and use the recommended protective equipment.
When to get help
Call a qualified pool professional when the water remains unsafe after testing, you cannot identify the product or test result, equipment is not circulating, or anyone has symptoms after a chemical exposure. For a spill or strong fumes, leave the area and follow the product's emergency instructions.
Sources and limits
This guide is general information, not a dosing prescription or diagnosis. See CDC water treatment and testing, CDC pool chemical safety, and CDC healthy swimming guidance.