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Differentiating stains and determining treatment

As organic debris (e.g. leaves, sticks, flowers and seeds) decay, it leaches tannins and other pigments that generally cause yellow or brownish stains on the pool’s surface.

By Karen Rigsby and Zach Hansen

Staining is a problem many pool and spa owners will contend with at some point. It is a nuisance that detracts from a pool or spa’s overall esthetic value and can contribute to surface deterioration. Staining can be prevented; however, the conditions, which ultimately cause it to happen must be recognized first.

Once an operator understands the mechanisms causing surface stains, common sense methods can usually be employed to avoid problems. However, there are also times when prevention fails. In these cases, treatments are available to remove stains and this is where identification becomes important. The ability to differentiate stains will help determine the specific treatment required, as well as shed light on the source of the contaminants causing the problem. If a pool operator knows the source, further preventive action can be taken.

Types of stain contaminants

The key to preventing pool and spa staining is understanding how and why they form. Stains can originate from either organic or inorganic contaminants.


These contaminants are introduced to the pool as organic debris from the surrounding environment. Plant matter, such as leaves, sticks, flowers, seeds or other materials drift into the pool and ultimately sink to the bottom and decomposes. As the debris decays, it leaches tannins and other pigments that generally cause yellow or brownish stains on the pool’s surface.


These contaminants are introduced into the pool from minerals that dissolve into water and dissociate into their metal components. These metals come from a variety of sources and cause coloured water or stains. The most common path of introduction is through pool source water.

Whether it is municipal or well water, all natural water sources contain dissolved metals. The amount and type, however, varies greatly depending on the region. Metals can also be introduced into the pool via products, such as copper algaecides or ionizers, or as a result of component corrosion. For example, metal parts, such as pump impellers, heat exchangers and filter components can be a source of metal contaminants causing stains. Thus, proper water balance is a contributing factor in controlling and preventing components from corroding and causing stains.

Organic staining

The best solution available for treating organic stains is to shock the water and brush the pool walls frequently. Always maintain the appropriate sanitizer residual and perform proper maintenance, including circulation, filtration and brushing or vacuuming surfaces. Stains that are organic in nature will fade over time with the appropriate care.

Inorganic staining

To better understand how metals can stain a pool one must understand their underlying chemistry. When dissolved in water, metals are present as positively charged particles called cations. Under certain conditions, the metal cations can chemically bind to negative anions, which cause the metals to drop out of solution (e.g. as a metal salt or mineral) and leave coloured stains on pool or spa surfaces. The oxidation process or alterations in water balance dictate when metals will precipitate and cause staining.

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  1. 1600 gal spa milk chocolate stain 100% ,motel ray pac heater ph7.4 alk125 fc3.0 CC 0 cya 0 plaster w lite blue color . Citric , absorbic , Hcl , sulfamic acids = no joy . Any ideas ???? Drained & refilled because CYA 400 ppm H2O is crystal but cannot move stain at all ! Mark 816-877-2510

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