STA POOL PLANT – CONTROLLING PH
Controlling pH W
Robbie Phillips and Richard Lamburn, STA’s Technical Pool Plant Team look at the control of pH – the key to safe, effective disinfection and comfortable, stable pool conditions
hat exactly is pH? ‘pH is the log of the reciprocal of the concentration of hydrogen ions in a volume of water’, or simply
a measure of the acidity or alkalinity of the pool water.
As the number of hydrogen ions in the solution increases, the pH decreases and the water becomes more acidic. Conversely, as the number of hydrogen ions in the solution decreases, the pH increases and the water becomes more basic.
pH is measured on a logarithmic scale which ranges from 0 (acids) to 14 (base), with 7.0 being neutral.
Keeping pool water within ideal pH ranges:
• Ensures effective micro-organism destruction
• Increases bather comfort • Prevents damage to the pool, its components and equipment.
Ideal pH levels depend on the other four components of water balance (total alkalinity, calcium hardness, water temperature and total dissolved solids), but typically range from 7.2 to 7.8, with an ideal of 7.2 to 7.6 – the lower part of the range the better while still maintaining correct water balance. Low pH levels can cause chlorine to dissipate rapidly. Equipment corrodes, and pool surface materials etch or crack. There is debate over lower pH levels as at the lower levels the disinfectant effect becomes greater. However, we will reach a point where bathing comes uncomfortable and the protection of water balance is compromised (corrosive). At high pH levels, less hypochlorous acid (HOCl) (disinfectant) forms and chlorine becomes less effective. Algae growth might increase, the water may cloud, scaling can occur and circulation pipes can calcify, and filter runs (the time between backwashing filters) often shorten. At high levels skin can be affected.
14 13
12 11
10 9 8 7
6 5
4 3 2 1 0
Most Alkaline Sodium Hypochlorite Calcium Hypochlorite
Sodium Carbonate (pH plus) Sodium Bicarbonate
Neutral Dichloroisocyanuric acid Lemon juice Carbonic acid (dissolved CO2 )
Dry acid (pH minus) Harpic toilet cleaner, Chlorine gas Conc. Hydrochloric/Sulphuric acid
Most Acidic
As you’ve probably noticed, pH levels fluctuate constantly. This problem is magnified if total alkalinity levels are permitted to drop.
Pool chemicals, rain, air pollution, the fresh make up water added to the pool, plaster and other pool surface materials and equipment the water comes in contact with, and waste products introduced into the pool by swimmers, all cause the pH to change. Some products like hydrochloric and sulphuric acid, cyanuric acid, sodium bisulphate, also trichlor tablets are acidic and all cause the pH to drop. Others, like dichlor or carbon dioxide are slightly acidic. While other chemicals like sodium and calcium hypochlorite, also sodium carbonate are alkaline. To keep pH in the proper range, the pool operator must test frequently using a photometric method and pH meter, and adjust as necessary.
COMMON PH ADJUSTMENT CHEMICALS Raise pH Sodium carbonate (soda ash)
As the number of hydrogen ions in the solution increases, the pH decreases and
the water becomes more acidic. Conversely, as the number of hydrogen ions in the solution decreases, the pH increases and the water becomes more basic”
www.swimmingpoolnews.co.uk
Tiling grout and screed can be destroyed by water lacking in calcium for example, often due to low pH levels. Corrosion of metal parts can cause leaks with potential undermining of pool structure
Lower pH Hydrochloric acid Sulphuric acid
Sodium bisulphate (dry acid) Carbon dioxide (CO2
)
The control of pH together with water balance can save substantial costs due to mainly corrosive water conditions. Tiling grout and screed can be destroyed by water lacking in calcium for example, often due to low pH levels. Corrosion of metal parts can cause leaks with potential undermining of pool structure. They can all potentially cause significant repair bills, together with expensive facility closures and loss of revenue.
STA 01922 645097
www.sta.co.uk
SPN October 2015 43
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60 |
Page 61 |
Page 62 |
Page 63 |
Page 64 |
Page 65 |
Page 66 |
Page 67 |
Page 68 |
Page 69 |
Page 70 |
Page 71 |
Page 72 |
Page 73 |
Page 74 |
Page 75 |
Page 76 |
Page 77 |
Page 78 |
Page 79 |
Page 80 |
Page 81 |
Page 82 |
Page 83 |
Page 84 |
Page 85 |
Page 86 |
Page 87 |
Page 88 |
Page 89 |
Page 90 |
Page 91 |
Page 92