An SI value of zero means water is properly balanced. No chemical adjustment is necessary if the SI is within ±0.5 units of zero; however, conditions producing a value greater than 0.5 may lead to cloudiness and scaling, while conditions producing a value less than -0.5 may cause corrosion of concrete or metal surfaces. (Note: While the cited SI range is commonly taught, the trend now in the pool/spa industry is to recommend a more restrictive range of -0.3 to 0.5 or even -0.3 to 0.3.)
