Algae spores are always present in swimming pools, and they can enter the pool through wind, rain, or even contaminated swimsuits and pool cleaning tools. Algae can bloom into a visible colony when conditions are right, such as poor water circulation, low flow or dead spots in the pool, poor water balance, low or inconsistent chlorine levels, short filter run times or an ineffective filter, and warm temperatures. The presence of nitrates, phosphates, and carbon dioxide can also spur their growth. Lack of maintenance, including inadequate filtration, out-of-balance water, and poor water sanitation, can also contribute to rapid growth. Organic material and bacteria can also contribute to algae growth, so regular cleaning and brushing of the pool walls and floor is essential. To prevent algae growth, it is important to maintain proper water balance, filtration, and sanitation, and to regularly clean and brush the pool.