Citric Acid to Remove Staining in a Pool

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Citric acid creates clean, unblemished pool surfaces.
Citric acid creates clean, unblemished pool surfaces. (Image: Jupiterimages/Pixland/Getty Images)

Even under the best care and maintenance programs, swimming pools occasionally become stained. This occurs due to a variety of reasons, including environmental conditions and time. When swimming pools become stained, often an acid wash is applied to remove these stains. Citric acid is used in pool acid washes, as it is safe and effective on pool surfaces, including concrete, fiberglass, acrylic and plastic components of a pool.

Citric Acid Explained

Citric acid is a weak acid that occurs naturally in citrus fruits. This acid is more environmentally friendly than most and acts as a cleaning agent for swimming pools. Citric acid removes the stained area of a pool when applied by eating away the top layer of the pool's surface. It does not harm a pool to have such a thin layer removed, it simply clears away the stain. Citric acid is a gentler stain remover than muriatic acid, another form of acid used to remove stains and resurface swimming pool interiors.

Types of Stains

Pool stains vary in appearance and source. Copper stains are blue and occur when copper strips from pool heater coils or a copper-based algaecide is used in the pool water. Iron stains are red and occur from iron levels in pool water, specifically water from wells. Black calcium stains occur from a mixture of pool chemicals and improper pH levels. Rust spots occur from fertilizer dropping into the pool water. These stains all penetrate the surface of the pool and are virtually impossible to remove without an acid wash.

Method

A citric acid wash is most effective on a swimming pool that has been cleaned, with all debris removed, after it is drained. The acid wash is applied from a watering can used for flowers. Fill the can with 1 gallon of water and then add 1 gallon of citric acid, always in that order. The pool walls are wetted with water from a hose and then the acid mixture is applied one area at a time and allowed to sit for 30 seconds before scrubbing with an acid brush and rinsing that section. Repeat around the entire surface area of the swimming pool, in sections. The leftover acid at the bottom of the pool is neutralized with baking soda before removal.

Warnings

Though citric acid is a gentler form of acid, it is still dangerous. Protective clothing must always be worn when working with citric acid. Improperly neutralized acid may kill animals, continue eating away at pool surfaces and injure humans. Citric acid also produces fumes that are harmful to humans and animals. This acid is an effective stain remover but seriously damages swimming pools when used improperly or when not rinsed completely away. Citric acid washes may be done by pool owners but are best left up to professional pool care experts.

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