Acid – A sour chemical substance containing hydrogen with the ability to dissolve metals, neutralize alkaline materials and combine with bases to form salts. Acid is used to lower (decrease) pH and total alkalinity of swimming pool and spa water. Examples are muriatic acid (hydrochloric) and dry acid (sodium bisulfate).
Acid Demand – Determined by the acid demand test. The amount of acid required to bring high pH and total alkalinity down to their proper levels.
Acid Demand Test – A reagent test usually used in conjunction with a pH test to determine the amount of acid needed to lower pH and total alkalinity levels.
Acid Rain – Precipitation having an unusually low pH value (4.5 or lower) caused by absorption of air polluted by sulfur dioxide, carbon dioxide and nitrous oxide.
Acrylic – A thermoplastic sheet formed into a mold to make a spa or related equipment. It is first heated and then vacuumed onto the mold.
Air Blower – A mechanical device that forces air through holes in the floor, bubbler ring or hydrotherapy jets in a spa.
Air-Relief Valve – A brass or plastic, manually operated valve located at the top of a filter tank for relieving the pressure inside the filter and for removing the air inside the filter (called bleeding the filter). Sometimes called a pressure-relief valve.