Water Maintenance

The primary reason for treating pool and spa water with sanitizing chemicals is to prevent the growth of bacteria which would make swimmers and bathers sick.
These bacteria can cause infections in ears, nose and throat and possibly other more dangerous diseases like Meningitis. Bacterial control is easily accomplished by adding a sanitizer (most commonly Hypochlorous Acid or simply Chlorine) regularly, and then passing the water through a filter to remove the dead bacteria. You then need to be sure that any additional bacteria entering the pool, is met by a sanitizer residual in sufficient concentration to kill this new bacteria as soon as possible.


The primary source of bacteria is the swimmers and bathers themselves. Animals can also contribute significantly to bacteria levels. A large dog may contaminate up to twenty times the volume of water that a human can.
While this all sounds pretty gruesome, it is generally accepted that most harmfull bacteria will be killed when exposed to a free chlorine residual as low as one milligram per litre or in other words one part per million (ppm). By regularly testing the water and adding the required amount of chlorine to the pool, a residual level of 1.0 or 2.0 ppm is easily maintained.
Water Balance
Untreated, or improperly treated water can be a health threat. Chemically balanced and sanitized water, on the other hand, will provide a healthy and visually appealing environment for you, your family and friends.
Balanced water means that chemical demands have been met. If the chemical levels are too low the water will aggressively seek the products it needs by attacking the pool surface and equipment. This may lead to severe corrosion problems. On the other hand, high chemical levels may lead to the formation of scale on the pool surfaces and equipment. Out of balance water can, therefore, cause expensive damage to the pool and may also inhibit the sanitizing process. In simple terms, the pool owner should balance the following variables :
pH
Total alkalinity
Clacium hardness
pH
pH is a measure of how acidic or alkaline the water is. The pH scale ranges from 0 to 14, with 7.0 being neutral. values below 7.0 are acidic, and values above 7.0 are alkaline. With pool water we are seeking a pH balance suitable to the pool user, the pool, and sanitizer used. Australian Standard 3633 defines the operating range as 7.0 to 7.8 and the recommended range of 7.2 to 7.6 (SPASA recommend 7.0 to 7.2 for fibreglass pools). Topping up your pool, heavy rain, heavy bathing loads and chemical additions can all change the pH level of your pool water. Incorrect pH levels can have the following effects : Cause swimmer discomfort (itchy skin, red eyes, etc.) Interfere with the action of your pool sanitizer. Effective sanitizing relies on pH values. Therefore, sanitizer and pH levels, should be the measures you check and adjust most often. Regardless of the chlorine type or the chlorination process used, any pH drift above the recommended range(7.0 to 7.8) will inhibit the sanitizing effect of your chlorine.
Total Alkalinity (T.A.)
This is a measure of bi-carbonates, carbonates and hydroxides in your water. The Standard recommends a range of 60 to 200 parts per million (ppm). Your pool builder or pool shop will advise you of the recommended level for your pool. Low T.A. will lead to erosion of the surface of concrete and painted pools. It will also cause the pH levels to be very unstable with small additions of chemicals resulting in major shifts in pH. This is sometimes known as "pH bounce". Total Alkalinity can be changed in the following ways : Adding buffer (bi-carbonate of soda). This raises the Total Alkalinity. Adding acid to your pool to lower pH will also lower Total Alkalinity. Topping-up your pool will change the Total Alkalinity depending on the T.A. of the top-up water. It can be seen that acids will lower the pH and Total Alkalinity. There is an interconnection between these two chemical components and, because of this, they need to be adjusted together. The levels you are seeking to maintain are : pH of 7.2 to 7.8 (7.0 to 7.2 - fibreglass pools) Total Alkalinity of approx. 100 to 120 ppm (60-200 is the recommended range). Check with you pool builder or poolshop for the level required in you pool. Lets assume that the pH is OK but the Total Alkalinity is low. To raise the level, add "buffer" (Sodium Bicarbonate) at the required rate. However, Buffer is an alkali and will also raise pH. Acid (Hydrochloric Acid or Sodium Bisulphate), which is used to lower pH, also lowers T.A. the trick is therefore to raise the T.A. artificially high so that when acid is added, to lower the pH to the correct level , the T.A. is also reduced to the correct range. Note : Hydrochloric Acid must always be diluted (one part acid to ten parts of water) prior to adding to the pool. Always add acid to water, never water to acid.
Calcium Hardness
In simple terms, this measures the amount of dissolved calcium in your pool water. The recommended range is 80 to 500 ppm. Both Total Alkalinity and Calcium Hardness need to be brought into balance. If not, low levels will mean the water is corrosive to the pool and/or equipment; high levels will lead to scale formation on pool and equipment. Calcium Hardness tests cannot usually be performed with the standard test kit. We suggest a water sample be taken to an NSPI Accredited Pool Shop for testing. A rough rule of thumb in areas where calcium levels are not naturally high is that testing annually will suffice after the initial adjustment. The only qualification to this is if you are using Clacium Hypochlorite to sanitize your pool. This chemical raises Calcium Hardness levels which may require more frequent testing and adjustment.
Tip....When adding chemicals it is best to add small quantities, leave for a few hours and re-test. Adding large quantities can result in big problems and big expense.
Types of Chlorine
Chlorine is available in a number of different forms. Granular, liquid or tablet, and can also be stabilized or unstabilized (Stabilizing refers to the combining of isocyanuric acid with chlorine to protect it from UV rays, which drastically reduce it's effectiveness). Chlorine can also be generated by a Salt Chlorinator. Each of these different forms has it's own features and benefits. For instance, granular chlorine is convenient, easy to store and relatively cheap, however it cannot be dosed automatically. On the other hand, liquid chlorine is bulky and can't be stored for long periods, but can be dosed automatically. All are satisfactory sanitisers for your pool, so choose the one that best suits your budget and lifestyle. No matter which form you decide to use, the requirement for a residual of 1.0 to 2.0 ppm remains the same.

Source : http://swimming.about.com