Water Treatment Chemicals
List of current popular products and processes with explanation of
how they work, advantages and disadvantages including:

Chlorine Gas
Sodium Hypochlorite
Calcium Hypochlorite
Chlorinated Isocyanurates (stabilized chlorine)
Bromine (BCDMH, DCDMH, and Sodium Bromide)
Ozonation
Active Oxygen
Copper / Silver
Biguanide (PHMB)
Ultraviolet (UV)
Algicides
pH control (acids (Including CO2) / alkalis (bases))
Alkalinity (levels and adjustment)
Calcium Hardness (levels and control)

Treatment Chemicals

Note that all disinfectant chemicals used for Pools and Spas are specifically for that purpose!
CHEMICALS MUST NEVER BE MIXED OUTSIDE OF THE SWIMMING POOL WATER UNLESS SPECIFICALLY DIRECTED TO DO SO!

Chlorine Gas

Liquified chlorine gas is the purest form of chlorine disinfection, it contains 100% of available chlorine. When chlorine gas reacts with pool water it produces free available chlorine and hydrochloric acid. This process causes the pH of the water to fall to below pH2 – highly acidic-requiring the continuous and automated addition of alkali in the form of sodium carbonate (soda ash) or sodium hydroxide (caustic soda) to raise the pH again. Chlorine gas is best suited for use in hard water areas where the natural hardness of the water helps to neutralise the acidity produced.
Chlorine gas must NEVER be used in residential pools.

Sodium Hypochlorite

Sodium hypochlorite is by far the most popular of the disinfectants used in swimming
pool water. It is a pale yellowish liquid with the characteristic smell of household bleach. The commercial product contains between 10 and 15% of available chlorine which is considerably more than the domestic product. Sodium hypochlorite is prepared by passing chlorine gas through a solution of sodium hydroxide under very controlled conditions. An excess of sodium hydroxide is left after the reaction to improve stability and this means that the solution has a very high pH – about pH 12. Even under satisfactory storage conditions – in the dark and at cool temperatures – sodium hypochlorite decomposes slowly, liberating oxygen and losing its available
chlorine content. Its pH however always remains high. Some blended solutions are available which contain stabilising agents to retard decomposition. These are usually nearer the 10% available chlorine strength and although they are more stable they still gradually deteriorate due to heat, light etc. It is generally recommended that during summer months storage is limited to a period of one month in dark containers at temperatures as cool as possible.

Important note
Never add acid directly to sodium hypochlorite solution as this will cause the production of chlorine gas. CAUTION: ALWAYS add chemicals to water. NEVER add water to a chemical as a violent action may occur.