Algae can appear as green slime in water or on pool liners and tiles. Algae are simple plant organisms that thrive wherever essential nitrogen, potassium and phosphorus are present. These elements, especially phosphorus, are common pool water contaminants that come from various sources including fertilizers, soil and tap water.
Often a significant amount of the slime is "pink slime," or methylobacterium, bacterial colonies that feed on organic material. These organisms have a slime coating that offers protection against many pool water disinfectants, making them difficult to eliminate entirely. They can establish themselves on most swimming pool accessories, including filters.
Mildew is a fungus that thrives in wet or damp environments, appearing as a whitish growth on the organic matter it feeds on. Mildew is unsightly, often malodorous, and frequently a health hazard. Swimming pools are ideal environments for mildew, which once established can cause pool liner stains that are difficult to remove.