The portion of total chlorine remaining in chlorinated water that is not combined with ammonia or nitrogen compounds and will react chemically with undesirable or pathogenic organisms; the amount of hypochlorous acid and hypochlorite ion in the water. ^

The state of being acidic (low pH) as opposed to being basic (high pH); measuring below neutral 7.0 on the pH scale. Aggressive Water

Microscopic forms of plant life that can inhabit a pool or spa. Some strains are free-floating; others cling to the pool or spa's surfaces. Algae spores thrive on sunlight, display a variety of colors and some strains can damage the pool's surface. Algaecide or Algicide

See Total Alkalinity.

Aluminum sulfate. A compound used to flocculate and sink small suspended particulate matter for removal by filtration or vacuuming. Available Chlorine

Small, single cell organisms that contaminate a pool or a spa. Bacteria can be introduced from the environment and by swimmers. Balanced Water

See Sodium Bicarbonate.

The state of being basic (alkaline), as opposed to being acidic; also, known as measuring above 7.0 on the pH scale. Broadcast

A member of the halogen family. Compounds of bromine are used regularly to sanitize spas. Bromide Reserve/Residual

The amount of dissolved calcium in the pool or spa water expressed as ppm or parts per million. Calcium Hypochlorite