Q. I have an in-ground pool with a vinyl liner. Are the dark spots in my pool black mold or black algae?

A. Black mold grows as a result of trapped moisture in the virgin soil behind the sides or under the sand floor in a vinyl-lined pool. Most often, the source of this problem is decomposition of soil and organic material under or behind the affected area of the liner. This mold shows up as black shadows behind the vinyl liner.

In the past, vinyl-lined pools used a sand floor. Today, sand is replaced with standard concrete or vermiculite (a lightweight, nonabrasive concrete) to help limit the occurrence of black mold in a vinyl-lined pool.

The cure for black mold is to remove the liner and treat the soil, usually during two or three days, for less than $200. Typically, sodium hypochlorite, or liquid chlorine, is applied to the soil before a new liner is installed. The new liner can cost between $1,800 and $3,500, depending on the size of the pool.

An extra measure can include placing a 2-millimeter-thick, protective membrane between the soil and the new liner to prevent the pool's temperature and moisture from affecting the soil behind the vinyl.

Black algae appears inside the pool and attaches to the vinyl surface. The proper treatment in a vinyl-lined pool is not large doses of chlorine as used in other types of pools because chlorine will bleach the liner's color and rob the liner of elasticity.

Instead, commercial-grade algaecides are added to eliminate the algae. Once killed by the treatment, the algae is easily brushed away. Liquid algaecide treatment should cost less than $75. Black algae can be controlled with proper water chemistry.

All pools should have daily chlorination, periodic shocking (overchlorination) of the pool and maintenance doses of algaecides.
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Jimmy McDonald
http://www.StartRemodeling.com
Jimmy@StartRemodeling.com

http://www.ToxicMoldUSA.com
McMoldMan@ToxicMoldUSA.com

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