Alkalinity is a measure of the ability of the water to resist changes in pH, this is also known as buffering. For the majority of applications, it is important to maintain a stable pH.
Alkalinity is made up of calcium and magnesium carbonates, bicarbonates, chlorides and sulfates, however it is conventionally always quoted as mg/L CaCO3.
Alkalinity can be measured as M-alkalinity, P-alkalinity and O-alkalinity. M-alkalinity, also known as total alkalinity, measures all the hydroxide, carbonate and bicarbonate ions. The P-alkalinity only measures the hydroxide and carbonate ions. The M- and P-alkalinity measurements together can be used to calculate the O-alkalinity which is a measure of the hydroxide ions.
Monitoring alkalinity in drinking water is important for both taste and for maintaining effective pH levels required for disinfection. Moderate alkalinity is desirable in most water supplies. Strong alkaline water has an unpleasant “soda” taste.
The EPA Secondary Drinking Water Regulations limit alkalinity only in terms of total dissolved solids (500 ppm) and to some extent by the limitation on pH.
Alkalinity is required to maintain effective biological activity and pH control. After complete nitrification, a residual alkalinity of 50 mg/L in the aeration tank is desirable. The process of nitrification uses up carbonates and bicarbonates and increases the acidity of the water. Monitoring of alkalinity is therefore important as the bacteria are highly sensitive to drops in pH.
Regular water testing in aquaculture is critical, one slight change in the water can be detrimental to a species. Aquatic life is very sensitive to pH changes; maintaining total alkalinity levels helps protect against rapid pH changes. To protect aquatic life, the alkalinity should be at least 20 mg/L, although this will depend on the fish present.
With one of the largest collections of aquatic life in the UK, the aquariums at the Zoological Society have interesting water quality demands. Read our case study Water Testing at London Zoo to find out more about alkalinity and other key parameters in aquaculture at London Zoo.
Alkalinity will prevent sudden pH changes when bodily matter is released into pool and spa water. Urine and sweat are acidic and can lead to pH changes if not correctly buffered. In pools and spas alkalinity should be measured at least once a week and the levels should be in the range 80 – 200mg/L CaCO3.
If the alkalinity is too low, pH can become unstable, and if the alkalinity is too high, the pH becomes difficult to change. For more information about managing alkalinity in your pool and spa download or pool chemistry guide or spa chemistry guide.
Water may be unsuitable for use in irrigation if the alkalinity level in the water is higher than the natural level of alkalinity in the soil. The alkalinity of irrigation water can affect plant growth, irrigation equipment and pesticide efficiency.
Palintest’s Pooltest 25 Photometer covers the complete range of water test parameters, making it ideal for professional pool and spa management. It enables full disinfection and water balance control. For spas and indoor pools the Pooltest 4 is the ideal compact photometer, with testing for: alkalinity, bromine, chlorine and pH. It can be used alongside a Palintest TDS meter to ensure full compliance with HSG 282. For more information on HSG282 and an introduction to spa chemistry watch our webinar here.
Nitrification is the conversion of ammonia to nitrate via the intermediate nitrite as part of the nitrogen cycle.
M alkalinity measures all the hydroxide, carbonate and bicarbonate ions.
The P-alkalinity only measures the hydroxide and carbonate ions.
The M- and P-alkalinity measurements together can be used to calculate the O-alkalinity, which is a measure of the hydroxide ions.