When building a pool, you will be faced with a choice between fully controlled or partially controlled Liquid Chlorine Pool or a Salt Water Pool, the two most common methods by which you can sanitise a pool. It should be noted that the sanitising agent that everyone calls chlorine is in fact the chlorine compound Hypochlorous Acid.
The choice comes down to having a pool with consistent accurate chemical levels (which is a controlled liquid chlorine pool) or an easier care pool (which is a salt water pool).
A Liquid Chlorine Pool is sanitised by the addition of liquid chlorine (sodium hypochlorite) either by hand or with the aid of a chemical controller. A Chemical Controller will pump chlorine (from a storage container) into the pool either at a pre-determined set rate or according to that needed in the pool as detected by a sensor probe. Liquid chlorine forms the required hypochlorous acid once added to the water.
A Salt Water Pool is sanitised by the manufacture of chlorine gas by means of the electrolysis of a chloride salt (usually sodium chloride). The chlorine gas reacts with the water to form hypochlorous acid. An electrolyte cell with its casing is plumbed into the filtration plumbing and the chlorine production is controlled by an attached control box which contains a transformer, timer and a printed circuit board which runs the system.
The major and most important difference between the two systems is the difference in the ability to control the chemical levels in a pool, especially when operating the controller in ORP mode (as against FAC mode). The liquid chlorine system with a quality controller can run a pool at minimal chemical levels. It can do this because the system also can respond to increased chlorine demand very quickly (provided the pump is big enough) which will occur when your system starts up (if running less than 24 hours a day) or, when a group of people jump into the pool. It will supply only what is needed. This is especially important to those of you who have chemical level concerns. When the pool is not in use the chemical demand will be low. Alternatively, with a salt water system, the chlorine production remains constant at the set point. Production will not respond to the increased chlorine required when there is a sudden increase pool usage. Because of the need to have sufficient chlorine in the pool during times of usage there will usually be excessive chlorine in the pool outside those usage times when the system does not have a chemical controller, which is the case in nearly all domestic pools. There are controllers that will turn a Chlorinator on and off according to chlorine demand as indicated by a chemical probe. In this situation the Chlorinator needs to be large enough to produce large amounts of chlorine over a short period of time. Again, pools that operate with a controlled Chlorinator need to have higher than necessary (but below the maximum) chlorine level in order to survive the initial demand for chlorine when a sudden increase in pool usage occurs. Correct selection of the Chlorinator size in the commercial pool environment will achieve these requirements.
Most chemical controllers that are used to dispense liquid chlorine also dispense hydrochloric acid to control the pH of the pool. The control of pH in a pool is necessary as there is a very important relationship between pH and sanitising power of chlorine (hypochlorous acid) in the pool. If the controllers did not also control the pH the chlorine usage would be much higher than necessary, and the Water Balance would be out of balance more often than not, which causes other problems. Very few domestic pool salt water chlorinators have pH control because it is difficult to do accurately. Quality top end chlorinator controllers can do this as these units contain some very clever science, resulting from years of research and, use gold tipped probes to achieve this control. Even then these controllers do not adjust the levels as quickly as they do when used in conjunction with liquid chlorine. Despite that, commercial salt water chlorinators combined with a quality controller do an excellent job and are especially good for commercial pools when an alternative to a liquid chlorine pool is preferable or even necessary.
Domestically, when choosing between a Liquid Chlorine Pool and a Salt Water Pool the things to consider are: –
Liquid Chlorine Pool with a chemical controller
Salt Water Pool with a domestic Chlorinator