Kevin Shea is senior vice president and chief marketing officer for Portland, Ore.-based Plastimayd LLC, a manufacturer of 

swimming pool liners.
Kevin Shea is senior vice president and chief marketing officer for Portland, Ore.-based Plastimayd LLC, a manufacturer of swimming pool liners.

Protected by special additives and coatings, vinyl pool liners are can withstand the extremes of sunshine, heat, cold and constant exposure to chemically treated water. But even the highest quality vinyl liner is subject to staining and bleaching.

Follow these simple, preventative steps to help ensure a stain-free liner.

One chemical at a time

Pre-dissolve sanitizers in a bucket of pool water and add the solution by pouring it through a sieve to catch any undissolved chemicals.

Any one chemical added to pool water should be allowed to circulate throughout the pool before adding a second chemical. The reason for this is that certain combinations of pool chemicals at high concentrations can cause bleaching.

The addition of a single chemical can damage a pool liner if it is not allowed to circulate sufficiently. Chemicals, such as chlorine, can settle in the deep end of the pool and bleach the liner if they are not allowed to circulate for several hours before a pool is closed for the season.

Spot bleaching of vinyl liners can also occur if undissolved particles of calcium hypochlorite or other slow-dissolving sanitizers are allowed to settle on the bottom of the pool. Using large, single doses of hydrochloric (muriatic) acid to adjust pH or total alkalinity levels can also damage vinyl liners. Because it is not sufficiently blended with pool water, the acid can chemically attack the liner’s printed pattern.

Source of the slime

A winter cover that tightly seals around the pool perimeter should be used to prevent the accumulation of organic debris such as leaves and insects during the winter months.

Organic debris staining can become a big problem, often presenting itself as a grayish mark. This happens most often after the pool is closed for the winter when debris might be allowed to accumulate over several months. But even when the pool is open, organic debris should not be allowed to sit on the vinyl, especially in the corners, because this could lead to staining.

In addition, under the proper conditions, fungi can grow on debris, producing a pink stain on the vinyl. Pink-colored blotches on vinyl pool liners are caused by a pigment excreted by bacterial microorganisms such as streptoverticillium reticulum. These microbes are metabolic products of various fungi and bacteria that can be affected by light, temperature, oxygen and pH.

Because the dye is highly soluble in vinyl, it easily migrates throughout the entire thickness of the liner. Dye on the surface of the liner can be bleached by chlorine — but new dye will simply migrate to the liner surface to replace it, making it seem as if the chlorine is having no effect on the stain.

Pink staining microorganisms can also develop on the underside of a vinyl liner. This growth may not take place directly on the liner itself, but on some other material touching the liner, such as soil or backing materials such as Styrofoam, felt or tape. Even though an antimicrobial agent is used in the vinyl formulation, the dye can migrate from unprotected components and cause staining in areas beyond the point of infestation.

If you must replace the liner

Remove all contaminated materials and disinfect the entire pool shell with a liquid chlorine spray or other suitable disinfectant.

Areas with a high water table, where the liner is always in contact with water full of microorganisms, can also cause pink or grayish stains on the underside of the liner. Using disinfectants at these sites may be ineffective, as they will be quickly washed away. One possible solution is to use a barrier — such as a layer of plastic sheet, or a layer of polyethylene between the pool shell and the liner or a barrier coating applied directly to the pool shell. The only known issue with this approach is the vinyl liner often will slide on the smooth surface of the polyethylene barrier, creating the potential for wrinkles.

When salt assaults

Many salt chlorinators leave stains in swimming pools regardless of their material.

When adding salt, make sure that the pump is running and that the salt is completely dissolved before turning it off. Test the water for pH and metals regularly.

If you need to use a stain-removal product, be sure to avoid phosphorus-based stain-fighters. These will cause a phosphate scale to grow in the chlorine generator.

Some of the best metal removers in the market are just simple filtering aids or sequestering agents.