Water Chemistry
Below is a summarization of the levels that are recommended by The Association of Pool and Spa Professionals (APSP) with the exception of phosphates. The phosphate information comes from www.naturalchemistry.com.
Total alkalinity is closely associated with pH but rather than a measure of hydrogen ion concentration it is a measure of the ability of a solution to neutralize hydrogen ions. Expressed in parts per million (ppm), total alkalinity is the result of alkaline materials including carbonates, bicarbonates and hydroxides - mostly bicarbonates. This acid neutralizing (buffering) capacity of water is desirable because it helps prevent wide variations in pH whenever small amounts of acid or alkali are added to the pool. Total alkalinity is a measure of water's resistance to change in pH.
Total alkalinity should be maintained in the range of 80 to 150 ppm.
Calcium Hardness
Calcium hardness is a measure of the dissolved calcium salts in water. Under normal conditions this should not be a problem in properly operated swimming pools. Estimates of the proper range of calcium hardness vary widely but the ideal level for plaster pool is generally considered to be about 250 ppm. If calcium hardness is very low then water may leach calcium from pool walls causing pitting of the plaster surface. Very high calcium hardness may contribute to scale formation and clouding of the water.
Chlorine
Chlorine is the choice sanitizer when it comes to everything from swimming pools to municipal waters. Chlorine is naturally a gas but is actually hypochlorous acid in water. It can be introduced through different vehicles: liquid, dry tablet form, powder form, gas injection or by salt (e.g. salt systems). An ideal level of chlorine (actually hypochlorous acid) is usually around 3.0 ppm.
Cyanuric Acid
Hypochlorous acid (aka "chlorine") is a highly unstable molecule which dissipates rapidly in the presence of sunlight. This results in considerable loss of free chlorine from pools exposed to sunlight. Proper stabilization of chlorine with cyanuric acid is essential and slows the rate of chlorine dissipation without appreciably sacrificing oxidation and disinfection activity.
In Southern California, outdoor pools should be maintained with 40 to 60 ppm of cyanuric acid.
Metals
The presence of metals is not desirable since they can potentially cause staining, especially for white plaster pools. The usage of metal-reducing products periodically are highly recommended to remove these potentially staining metals. Some algaecides contain, and are based on the action of, certain metals to eliminate algae and microbes (e.g. copper and silver algaecides).
pH
pH is the single most important element in swimming pool water chemistry. It affects every other chemical balance in pool water.
pH is a measure of hydrogen ion (H+) concentration in water. It indicates the relative acidity or basicity of pool water. pH is measured on a scale of 0 (strong acid) to 14 (strong base) with 7 being the neutral pH.
In pools, a slightly alkaline pH of 7.4 to 7.6 is most desirable because this range is most comfortable to the human eye and provides for optimum use of free chlorine while maintaining water that is not corrosive or scale forming.
pH must be maintained between 7.2 and 7.8.
Phosphates
Phosphates are salts of phosphoric acid. Phosphoric acid (H3PO4) is the acid produced when phosphorus is dissolved in water.
Phosphates, which contain phosphorus, are plant nutrients that can also be a pollutant. Phosphates in water contribute to algae blooms in the same way nitrates do. In fact, phosphorus is often the “missing ingredient” limiting the growth of algae. Two other nutrients required by algae for cell division and growth are nitrogen and carbon dioxide, both of which are generally in ready supply. Phosphorus in the soluble orthophosphate form is utilized and taken up by plants for growth. Increasing concentrations of available phosphorus allow plants to assimilate more nitrogen before the phosphorus is depleted. Thus if sufficient phosphorus is available, normal to elevated concentrations of nitrates will lead to an algae bloom.
Studies have proven conclusively that phosphates are the limiting nutrient for algae growth. The greater amount of phosphate present in water, the greater amount of inhibitory product ie: sanitizer and / or algaecide is necessary to prevent algae growth. The amount of phosphate present in a body of water will also determine how much algae can be grown. The greater amount of phosphate, the greater the potential for algae growth and severity of the bloom.
Salt
This test is only for swimming pools or spas which use a salt water chlorination system. This level or range can vary depending on the exact system.
Saturation index
The saturation index (Si) relates to the calcium and alkalinity in the water and is an indicator of the pool water "balance". The Si is a useful tool and must be calculated with the appropriate formula. Your water is properly balanced if the Si is 0 ±.2.
If the Si is below -0.2, the water is corrosive and plaster pool walls will be dissolved into the water. If the Si is above +0.2, scaling and staining will occur.
Stabilizer
Total Dissolved Solids (TDS)
After a pool has been in use for a time, dissolved solids may begin to accumulate. These unfilterable solids include minerals, salts, body wastes, suntan lotion, stabilizer, chlorines, algicide, dirt, pollen, etc. Tap water used to fill the pool also contains dissolved solids (which significantly contributes to this accumulation). Most pools should be drained after 3 to 5 years, if they reach 2500 ppm of total dissolved solids or if they gain 1500 ppm of total dissolved solids above the start-up level.
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