A major factor in vinyl-liner pool care that should be considered is air temperature, which has a profound effect on water. Package-pool veterans say to keep free chlorine levels between 1.0 and 1.5 ppm when the temperature is below 70 degrees, and between 3 and 5 ppm if it is above 70. If the level drops lower than 1.0 ppm, algae blooms and unchecked bacteria growth may occur.

This is not only unhealthy, but it also can cause stains to appear on the liner. The problem can be further exacerbated if it’s accompanied by a pH level that drops below the 7.0 mark. This could become a bigger problem when service companies close a vinyl-liner pool for the winter. With the temperature changes, you run more risk of the vinyl cracking. But typically if close it for the winter with the water balanced, it will be the same when you open it back up.

Acids used in pool care — the stabilizing type and those used for pH adjustment — should be taken into account as well. Because chlorine levels are depleted by ultraviolet light, the water needs to be stabilized with cyanuric acid. Recommended ranges are 30- to 100 ppm.

Some experts suggest avoiding the use of muriatic acid for pH adjustments. The acid can attack the liner pattern and make it more susceptible to abrasion wear. Instead, use sodium bisulfate to bring the pH into the desired range.

Just like shotcrete and gunite, vinyl liners are susceptible to staining due to metals falling out of solution and precipitating across the pool surface. Experts say to check for metals in the source water. If metals are present, monitor their levels on a monthly basis. If there are no metals, check every six months.

If your readings indicate that mineral levels  — especially copper and iron — are rising, you may need to incorporate a chelating agent to remove the metals from the water. Follow the manufacturer’s instructions closely.

If discoloration has already occurred, use a stain remover that has been created for vinyl. Whatever product you use, make sure it states specifically that it can be used with vinyl-liner pools.