Algae - microscopic forms of plants that grow in the water and cause discoloration.

Algaecides - chemicals that prevent and control algae growth.

Bacteria - microscopic organisms (germs) that can cause illness.

Chelating Agents - chemicals that combine with dissolved metals to prevent water discoloration and stains.

Chlorine - the most commonly used disinfecting agent for swimming pools.

Chlorine Demand - the amount of chlorine needed to destroy bacteria, algae, chloramines, and other swimming pool contaminants.The chlorine demand must be satisfied before a chlorine residual is available to disinfect the pool water.

Chlorine Residual - the chlorine level in the water after the chlorine demand has been satisfied. The free available chlorine is the true measure of chlorine disinfection.

DPD - an indicator tablet used to measure the free available chlorine residual. Turns red pink in presence of chlorine.

Dry Acid (Sodium Bisulfate) - a granular material used to lower the presence of chlorine.

Free Available Chlorine - that portion of the total chlorine remaining in chlorinated water that is not combined with ammonia or nitrogen compounds and will not react chemically with undesirable or pathogenic organisms.

Hardness - The amount of calcium or magnesium dissolved in the water. High levels may contribute to scale deposits.Low levels may lead to corrosion and etching of plaster pools.

Hypochlorous Acid - The most powerful disinfecting form of chlorine in water.

Muriatic Acid - a liquid used for lowering pH or total alkalinity.

pH - Measurement of the acidity / alkalinity of water. Readings above 7 are alkaline: readings below 7 are acidic.

ppm - parts per million. Example: one penny in $10,000 equals 1 ppm.

Phenol Red - the indicator solution that measures pH.

Scale - a precipitate that forms on surfaces in contact with water when the pH level, Total Alkalinity and/or Calcium Hardness are too high.

Shock Treatment - the addition of 5-10 ppm of free available chlorine, in response to a particular pool problem such as algae.

Stabilizer (Cyanuric Acid or conditioner) (s-triazinetrione), also called Isocyanuric Acid. A chemical that helps prolong the useful life of chlorine in the water by slowing down chlorine decay due to sunlight.

Total Alkalinity - Acts as a buffer to pre-vent changes in pH.

Total Chlorine - The sum of free available chlorine and combined chlorine.