and water quality Since some hot tubs are not drained after each use it is necessary to treat the water to keep it attractive and safe. It must be neither too alkaline nor too acidic, and must be sanitised to stay free of harmful microorganisms. Partly due to their high water temperatures, hot tubs can pose particular health risks if not regularly maintained: outbreaks of Legionnaires' Disease have been traced to poorly sanitized hot tubs. Typically chlorine or bromine are used as sanitizers, but salt water chlorination is starting to become more common. Hot tubs should also be periodically shocked,Hot Tub Shock is a chemical sanitizer used to treat water in spas and hot tubs. It is with chlorine, bromine-based, or non-chlorine shock products that kill bacteria, germs, and other contaminants in the water. Hot Tub Shock helps maintain the pH balance of hot tub water, reducing odors and discoloration as it improves sanitization levels. Sanitation can also be aided by a non-chemical ozonator. For aesthetic reasons, and for the sanitizer to work properly, water should be neither too alkaline nor too acidic (low pH). The hardness level of the water, measured as the amount of dissolved calcium, is also important. Insufficient hardness can lead to corrosion and water foaming.The ideal range of calcium hardness levels in a hot tub or spa water should be between 150 and 250 ppm (parts per million) Types Portable vinyl-liner hot tub: these are cheaper and smaller, and require less power, e.g. 110–120 V 15 A household power circuits in North America. Roto-molded hot tubs are constructed with the shell and surrounding cabinet as a single piece. They have molded seating. Acrylic: these hot tubs have a cast acrylic shell, supported by a frame structure, and are usually surrounded by a skirt of either cedar or simulated wood-grain plastic. They typically can seat two to seven persons or more. Cement: hot tubs can also be built of cement, above-ground, or in-ground like a small swimming pool. Wooden hot tubs: round wooden hot tubs peaked in popularity in the 1970s, having now been replaced by modern construction methods. Wooden hot tubs are often made of redwood or cedar and assembled from vertical staves and the structure is held together like wooden barrels, with metal bands. Stainless steel hot tubs can be made in any shape and size and are extremely durable. Fiberglass hot tub: glass-reinforced