| HALOGENS
 
(chemical related) 
The chemical elements either individually or collectively that constitute Group 
VIIB of the Periodic Table of Elements: fluorine, chlorine, bromine, iodine and 
astatine. Of these, only chlorine and bromine are used as disinfectants and 
sanitizers in pools and spas.
 HAND RAIL A tubular steel 
or plastic device that can be gripped by swimmers or bathers for the purpose of 
steadying themselves. Usually located near the steps in the pool.
 HAND SKIMMER  A 
screen attached to a frame which is then attached to a telepole used to remove 
large floating debris, such as leaves and bugs, from the water's surface.
 HARDNESS
 
(chemical related) 
The amount of calcium and magnesium dissolved in the water. "Water" or "total" 
hardness refers to the total magnesium and calcium dissolved in the water. 
Calcium hardness refers to just the calcium. Measured by a test kit and 
expressed as ppm. The proper range is 200 to 400 ppm.
 HEAT EXCHANGER A device 
located inside the heater providing for the transfer of heat from the heat 
source to the water. This is usually a series of metallic tubes with fins 
located just above the flames.
 HEAT PUMP  A 
refrigeration compressor, usually electrically driven, that is operated in 
reverse. To obtain heat, the evaporator side (cooling coil) is exposed to water, 
air or ground. The coil takes the heat from this source and transfers it to the 
condenser coil where it discharges the heat to the pool or spa to be heated.
 HEATER A fossil-fueled, 
electric or solar device used to heat the water of a pool, spa or hot tub. HERBICIDE
 
(chemical related) 
A chemical compound used to kill or control plant growth or algae. Simazine is a 
common pool herbicide.
 HORSEPOWER The work done 
per unit of time. 1 horsepower equals 33,000 foot-pounds of work per minute or 
approximately 746 watts. Motors for pumps are rated in horsepower.
 HOT TUB A spa constructed 
of wood with the sides and bottom formed separately and joined together by 
hoops, bands or rods.
 HYDROCHLORIC ACID  
(chemical related)  
Also called muriatic acid - A very strong acid used in pools to lower the pH and 
total alkalinity. It can also be used for various cleaning needs. Used in "acid 
washing" a pool. Use extreme care in handling.
 HYDROGEN
 (chemical related) 
The lightest chemical element. A component of water, and a frequent product of 
many chemical reactions. pH is a measure of hydrogen in its ionic form in water.
 HYDROGEN ION  
(chemical related)  
The positively charged nucleus of hydrogen atom. The relative degree of acid or 
base of a solution (called pH) is a measure of hydrogen ions.
 HYDROGEN PEROXIDE  
(chemical related)  
An unstable, colorless, heavy liquid used as a bleach in industry and as an 
antiseptic in households. It is used as an oxidizing agent in pools and spas. 
May also be used to de-chlorinate pool or spa water.
(also see biguanide)
 HYDRO-JET A fitting in the 
pool or spa on the water return line from the equipment that blends or mixes air 
and water, creating a high- velocity, turbulent stream of air-enriched water.
 HYPOBROMOUS ACID  
(chemical related)  
The most powerful disinfecting form of bromine in water. Sometimes called the 
killing form of bromine.
 HYPOCHLORITE
 
(chemical related) 
The name given to a family of chlorine- containing compounds, including calcium 
hypochlorite, sodium hypochlorite and lithium hypochlorite, that are used as 
disinfectants and sanitizers in pool and spa water.
 HYPOCHLOROUS ACID  
(chemical related)  
The most powerful disinfecting form of chlorine in water. Sometimes called the 
killing form of chlorine. 
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