About Chlorine
Jun 21st, 2007 by admin
In its elemental state, chlorine exists as a gas. Gas is available for swimming pool sanitation; is very cheap, and is the purest form of chlorine, with no binders or carriers. The % of available chlorine is 100%. It is also extremely dangerous and restricted in its use. It is rare to find a pool using gas as it’s sanitizer, and those that do are usually very old, very large public pools that have (we hope) enacted strict safety procedures. Gas is very acidic, with a pH close to muriatic acid, so these pools using it add a lot of base to counteract this.
Liquid chlorine is another type which is created by bubbling the chlorine gas through a solution of caustic soda. The yellow liquid (stronger, but chemically identical to bleach) has 10-15% available chlorine, and has a pH on the other end of the scale at 13. Liquid Chlorine is called Sodium Hypochlorite (NaOCl) and because it is already in solution, sodium hypo produces hypochlorous acid instantly when it contacts water. The liquid can be poured directly into the pool, but it is recommended to use a diaphragm or peristaltic pump. The use of liquid chlorine is more dominant in larger commercial pools which have it delivered into 55 gallon vats. For most residential pools, its lower cost seems to be outweighed by its difficulty in use and the amount of acid required to counteract its pH of 13. Use care when handling as this chemical is corrosive to just about everything.
Trichlor is a tablet form of chlorine, and is short for Trichloro-s-triazinetrione, a stabilized form of chlorine that has achieved a great amount of use in the last ten years. “Stabilized” means that it has cyanuric acid pressed into the tablet. Cyanuric, also called stabilizer or conditioner, is like sunscreen for the chlorine molecule; an extender, if you will. Trichlor is created by combining the salts of cyanuric acid and chlorine gas into a tablet or stick, and is 90% available chlorine. The pH is somewhat low at 3, so the pH in your pool may gravitate downward. This form is slow dissolving, and so it works well in floaters or in-line erosion feeders. Using tablets in the skimmer is not recommended, because of the corrosive nature of the chemical contacting metal pipes and equipment. This becomes more of a problem when the filter pump is operated on a timer. It has been known to strip out the copper inside of a heater. (An effective, yet expensive means of controlling algae). Tablets should also not be thrown directly into the pool, they can stain and etch plaster and bleach and deteriorate vinyl.
Another member of the chlorinated iso-cyanurate family is Dichlor, short for Sodium Dichloro -s-triazinetrione. Dichlor is made in roughly the same manner as trichlor, however the product is much different. The pH is a very acceptable 7, and it is manufactured in the form of granules, so it dissolves rapidly and goes right to work on contaminants. Dichlor has less chlorine, pound per pound at only 62% available chlorine. Because it contains cyanuric acid, it lasts longer than other unstabilized forms of granular chlorine. It can be used as a shock treatment oxidizer, or for normal sanitation. Dichlor’s main drawback is it’s cost per pound of available chlorine. It is perhaps the most expensive form of chlorine available.
There are two other types of granular chlorine on the market - the hypochlorites. Lithium Hypochlorite, like dichlor, is a very expensive product. At only 35% available, it takes almost 3 lbs of lithium to equal one lb of trichlor and its pH of 11 will require additions of an acid to adjust the pool water. It’s main advantages are that it is calcium free, and so it won’t contribute to hardness levels; it’s dust free and non-flammable. It dissolves extremely quickly, before it hits the floor, so its use is safe in vinyl liner pools. Lithium can be used for either shock treating or for regular chlorination.
Calcium Hypochlorite is commonly available in is granular form, but can also be purchased in tablet form. Cal Hypo is a commonly used shock treatment throughout the country. Although not stabilized with cyanuric acid, it has a quick kill rate against algae and chloramines, and has 65% available chlorine per lb. Some other granular forms of chlorine are more powder like, and thus dissolve more rapidly than the larger granules of cal hypo. It’s a good idea to pre dissolve cal hypo into a bucket of water prior to adding it to a pool. It’s popularity is due mainly to its availability and low price, despite a high pH value of nearly 12, and the calcium binders used which contribute to higher hardness levels. Cal hypo is more dangerous and unstable than other forms in that it is very dusty and becomes contaminated easily by foreign substances which can cause combustion. Mix only with water, don’t breathe the dust, and keep the lid tightly secure and clean.