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If small clumps of algae form but do not spread to the rest of the pool, you may have areas of stagnant water. Check that your water jets are functioning properly. They should point into the water at an angle, so the water moves in a spiral pattern. A flocculant or coagulant clumps the algae together, making it possible to vacuum living algae. This may take a hard day of work, but your pool should be clear by the end of it. This is the fastest way to get your pool looking good, but it does not make the water safe to swim in. If algae can multiply, so can viruses and bacteria. Follow this with a chlorine shock treatment to sanitize the pool, and do not swim in the pool until chlorine and pH levels are back to normal. Algaecide will certainly kill your algae, but the side effects and expense may not be worth it. Here are a few factors to weigh when considering this option: Some algaecide products are not powerful enough to treat an existing bloom, especially if you have black algae as well. Ask a pool store employee for help, or find a product with 30%+ active ingredients. Quaternary ammonia algaecides ("poly quats") are cheap, but cause your water to foam. Many people find this annoying. Copper-based algaecides are more effective, but expensive. They usually stain your pool walls as well. After adding the algaecide, wait at least 24 hours before adding other chemicals.
Improve circulation to handle small spots of algae. Gather the algae with a flocculant. Treat the pool with algaecide.