In Northern latitudes, active oxygen is a particularly popular alternative disinfectant to chlorine. Principally, however, for purposes of measurement what counts is whether the medium used contains persulfate or peroxide. Water disinfected with persulfate-containing media is measured according to the DPD N° 4 method. When using peroxide containing disinfection media, Hydrogen Peroxide tablets are used in connection with the Acidifying PT tablets. In both cases, the “Active Oxygen (O2)“ designation is in fact misleading. It is not the molecular Oxygen that oxidizes (disinfects); rather it is an Oxygen radical which quite quickly combines with an additional radical to form molecular Oxygen (the air one breathes). This is also the main disadvantage to this method; because the disinfection effect does not last long and the effect is rather limited. As a strict rule, therefore, Chlorine is added in regular intervals when Active Oxygen is used for disinfection. Yet with the DPD N° 4 method false readings can then result (when simultaneously using both Chlorine and Active Oxygen), because the potassium iodide contained in this tablet catalytically splits the persulfates and thus the sum of persulfate and chlorine is indicated
KS4,3 Acidity is also known as m-Alkalinity, Total Alkalinity, Hydrogen Carbonate Hardness, Acid Buffering Power, Temporary Hardness, … Alkalinity describes the ability of water to buffer the increase of ph value influencing chemicals (flocculants, disinfection media – e.g. chlorine products – lowering or raising pH). To provide a sufficient buffering effect, alkalinity should amount to at least 0.7 mol/m3 and/or mmol/l. This value represents the hydrogen carbonated materials dissolved in water. The buffering effect in the 4.2 – 8.2 pH range relies on a balance between hydrogen carbonate ions and carbon dioxide dissolved in water. Should chemicals that lower the pH value of water be added (acids), then the hydrogen carbonate ion combines with these to form carbonic acid (which in turn dissolves into carbon dioxide and water) and water. At a 4.3 pH value all hydrogen carbonate ions are depleted; thus the KS4,3 Acidity designation. Should in contrast chemicals be added that raise the pH value (bases), then hydrogen carbonate ions form again out of dissolved carbon dioxide and water. The modified relationship between dissolved carbon dioxide and hydrogen carbonate ions thus determines a new pH value. The buffering capacity of water becomes too low at alkalinities below 0.7 mmol/l, thus making it difficult to determine the pH value. In such cases small amounts of acids and bases will immediately and intensively change the pH value. Furthermore, water will have a corrosive effect on pipe mains. An alkalinity value which is too low can be increased through the addition of sodium hydrogen carbonate and/or sodium carbonate. When alkalinity values are high, however, the buffering effect is too large and large amounts of pH regulators are needed in order to achieve a change in pH. Additionally, when conditions are unfavorable (warming, pH > 8.2), calcium tends to precipitate because carbonate ions form out of hydrogen carbonate ions which in turn form water-insoluble compounds in the presence of calcium or magnesium (see Total Hardness). Alkalinity that is too high can be corrected through – at least partial – replacement of water. Because pH values above 8.2 will stop the equilibrium between hydrogen carbonate ions and carbonate ions, the alkalinity of the water must then (pH value over 8.2) be measured with the Alkalinity-P method.
Using bromine as a disinfectant is becoming a popular alternative to chlorine. The advantage of this method is that combined bromine is unscented compared to combined chlorine (chloramine). That is, the disinfection effect is the same but human mucous membranes are not irritated. Disadvantages to the use of bromine products include, however, the limited oxidation effect and the higher prices and handling risks. Often a combination of bromine and chlorine is used; but this makes determining the concentration difficult. Under the DPD N° 1 method, measurements now show (if chlorine is used with bromine) the total concentration of free and total bromine and free chlorine. In order to establish the bromine concentration in this special case, the free chlorine must be converted into combined chlorine with the aid of DPD-glycine. In contrast to chlorine, the confirmation 'DPD N° 1' reagent works with both free and combined bromine, thus always establishing the total bromine content.
Chlorine (in the form of sodium hypochlorite, calcium hypochlorite, chlorine gas, chlorinated isocyanurates,...) has become the leading disinfectant for swimming and bathing pool water worldwide. When measuring the chlorine concentration present in the water, a distinction is made between 3 partial values according to DIN EN 7393. 1 Free chlorine: Chlorine present as hypochlorous acid, hypochlorite ion or as dissolved elemental chlorine. 2. Combined chlorine: Proportion of total chlorine present in the form of chloramines and all chlorinated derivatives of organic nitrogen compounds. 3. Total chlorine: Sum of the former two forms. While free chlorine is immediately available for disinfection action, the disinfection potential of combined chlorine is severely limited. The chloramines are responsible for the typical indoor pool odor and the irritation of human mucous membranes, resulting in reddened eyes. A representative of this class of substances is nitrogen trichloride, which is already perceived by humans at a concentration of 0.02 mg/l. Free chlorine is measured according to the DPD N° 1 method. The indicator chemical N,N-diethyl-p-phenylenediamine sulfate (DPD) is oxidized by the chlorine and turns red. The more intense the discoloration, the more chlorine is present in the water. The chlorine concentration can now be determined by photometric measurement or optical comparison with a color scale. If a DPD N° 3 tablet is now added to this sample, the bound chlorine is also displayed. The measured value therefore now corresponds to the total chlorine concentration. The concentration of combined chlorine corresponds to the difference between total chlorine and free chlorine. Since even the smallest traces of the effective chemical of the DPD N° 3 tablets cause combined chlorine to become effective in the measurement, it is essential to ensure that the measuring device is cleaned extremely carefully before the next DPD N° 1 measurement in order to avoid a measurement error. The use of two different measuring vessels (one generally for the measurement of free and one generally for the measurement of total chlorine values) would be recommended.
Chlorine dioxide (2.33 times heavier than air) is known as a gaseous compound of the halogen, chlorine, and oxygen (ClO2); which has the advantage over pure chlorine that it effects smell and taste perception less and that is also acts as an anti-virus. Chlorine dioxide is also manufactured at special facilities near the production site by combining chlorine gas and/or under-chlorinated acid and a fluid sodium chlorite solution (NaClO2) (10:1). On average 0.05 mg/l – 0.2 mg/l are assumed as average minimum/maximum values.
When using organic chlorine products (trichlorisocyanuric acid and sodium dichlorisocyanurate), the so-called 'isocyanuric acid' creates the carrier for chlorine. While the advantage of organic chlorine products clearly lies in the higher portion of active chlorine (up to 90%), the isocyanuric acid carrier substance can limit the speed at which the chlorine can kill off the bacteria when the concentration in water is high (>50 mg/l). It is thus recommended that one measure the cyanuric acid just as regularly as the chlorine content of the pool, in order not to counteract this fact by adding more chlorine (thus leading to higher isocyanuric acid being added).
Basically dissolved salts belonging to the alkaline earth elements calcium and magnesium are found in non-distilled water. In rare cases, strontium and barium can also be found. These combine with carbonate ions to form water- insoluble compounds (calcium). Through the total hardness measurement, the potential danger of calcium precipitation is measured as the required carbonate ions form from hydrogen carbonate ions when water heats up or when there are pH values that are greater than 8.2 (comp. Alkalinity). When measuring calcium hardness (SVZ1300 tablet process), only the part of the dissolved calcium in water is measured. The amount of magnesium dissolved in water is determined from the difference between the measurement and the total hardness.
In Northern latitudes, active oxygen is a particularly popular alternative disinfectant to chlorine. Principally, however, for the purposes of measurement what counts is whether the medium used contains persulfate or peroxide. Water disinfected with persulfate-containing media is measured according to the DPD N° 4 method. When using peroxide containing disinfection media, Hydrogen Peroxide tablets are used in connection with the Acidifying PT tablets. In both cases, the “Active Oxygen (O2)“ designation is in fact misleading. It is not the molecular Oxygen that oxidizes (disinfects); rather it is an Oxygen radical which quite quickly combines with an additional radical to form molecular Oxygen (the air one breathes). This is also the main disadvantage to this method; because the disinfection effect does not last long and the effect is rather limited. As a strict rule, therefore, Chlorine is added in regular intervals when Active Oxygen is used for disinfection. Yet with the DPD N° 4 method false readings can then result (when simultaneously using both Chlorine and Active Oxygen), because the potassium iodide contained in this tablet catalytically splits the persulfates and thus the sum of persulfate and chlorine is indicated.
Ozone is comprised of 3 oxygen atoms (O3). It is an unstable molecule and disintegrates, after a rather short time either in the air or when it is dissolved in water, into oxygen, O2 and an oxygen radical. The oxidative effect of this oxygen radical is very strong and a depot effect is ruled out because two radicals immediately combine to O2. Ozone is produced directly on the spot by ozone producers and other required appliance-like devices. Special rules and precautions are required, because Ozone is 10 times more poisonous than chlorine. Thus Ozone is only used during a single dosage stretch – outside the pool – and must be filtered out before being used again (activated carbon). The maximum allowable concentration of ozone added to the pool is only 0.05 mg/l which is why ozone is insufficient as a disinfectant requiring it to be supplemented by other – as a rule chlorine content – disinfectants. Ozone kills bacteria, oxidizes organic contamination (e.g. urea), reduces chlorine usage, and leaves no irritating traces behind. As a rule, the human nose which can perceive ozone concentrations of 1:500.000 is the best measuring device. However, ozone combined with chlorine can be measured under the DPD method. By adding glycine, ozone is eliminated so that chlorine alone can be measured whereby the ozone content is determined from the difference.
The pH (potentia Hydrogenii) value is a measure of the strength of the acidic and/or base effect of a watery solution. It is particularly important when preparing bathing water because, among other things, it influences the effectiveness of disinfectants and the compatibility of the water with skin, eyes, and materials. A pH value of 5.5 is ideal for the skin. However, the water would then have so much acid that metallic materials would not only corrode but eyes would start to burn because tears have a pH value of between 7.0 and 7.5. therefore, a compromise must be found. In regard to materials compatibility, the pH value shouldn’t fall below 7.0 in any case. At the same time pH values over 7.6 will have dermatological effects and will also influence the effectiveness of the disinfectant, thus negatively influencing the speed at with which bacteria can be killed off. Principally: At pH values above 7.5 = the natural coat of the skin that protects against acids begins to be destroyed (>8.0); in (medium) hard water, calcium precipitation beings (>8.0); the disinfecting effect of chlorine declines with (>7.5) pH values under 7.0 = chloramines form which irritate the mucous membranes and cause irritations to the sense of smell (<7.0); corrosion appearances in metal-content (installed) parts (<6.5); problems with flocculation (<6.2).
Urea is an organic contaminant that is mainly introduced into the bath water through human excrements such as urine or sweat. The concentration increases with a high bathing volume or through heat. Urea itself is a crystalline and colourless compound which is completely soluble in water. In water, urea is decomposed by enzymes or bacteria present in the water to CO2 and ammonium. However, the decomposition can also be oxidative. Although urea itself is odourless, so-called chloramines are formed during oxidation with a disinfectant such as chlorine, which are responsible for the characteristic chlorine odour and are also known as bound chlorine. Since active chlorine is consumed in the reaction, a subsequent dosage of the disinfectant may be necessary. Urea is therefore a good indicator of the degree of contamination of bathing water. The detection method is enzymatic, therefore the PL Urea 2 Reagent must be stored at 4°C - 8°C and the sample must be measured at 20°C - 30°C water temperature.
Biguanide disinfectants are also gaining in popularity as an alternative to chlorine. Other than with other substitute materials, such as for example ozone or active oxygen, biguanides do not go well with chlorine, bromine, copper, or silver compounds. Nevertheless a counteracting agent is required because biguanides do not deploy an oxidative effect which is required, for example, for the breakdown of organic materials such as ureas and sweat. To do this, as a rule, hydrogen peroxide (H2O2) is used in addition to biguanide.