Basic Swimming Pool Water Chemistry
By Brian Barker
Pool pH & Pool Alkalinity
The pH and Alkalinity levels of swimming pool water affect many areas of the swimming pool and must be kept at the correct levels if you expect to successfully maintain your swimming pool. The Alkalinity of pool water acts as a buffer for the pH, and helps prevent the pool pH level from fluctuating. The Alkalinity should be maintained at 80 - 120 ppm. The pH is the measure of the acidity of the swimming pool water, and the pH level should be maintained at 7.2 - 7.6 ppm. The pH of pool water is somewhat sensitive, but easily controlled if the Alkalinity is kept in range. All basic pool test kits should read the pH and Alkalinity level of pool water, and these levels are easily adjusted with common water balancing pool chemicals. If the pool pH level is not kept in range pool water may irritate the skin and eyes of swimmers, corrode the pool surface and inside of the pool equipment and make it very hard to maintain the chlorine level of the swimming pool.
Pool Chlorine Stabilizer
The chemical name of pool “Stabilizer” is Cyanuric Acid and it is referred to by either title. The Stabilizer level of swimming pool water must be maintained at 30-50 ppm. The Stabilizer level is important, but is typically only tested at the beginning of the swimming season when a pool is opened. The Stabilizer in swimming pool water partially surrounds the chlorine on a molecular level, to protect the chlorine and prevent the chlorine from being quickly burned off and used up by the sun.
The symptoms of having too much Stabilizer or too little stabilizer in your pool water are very similar, and if you experience problems maintaining a chlorine level when all other chemical levels are properly balanced the stabilizer level should be tested. If the Stabilizer level tests lower than 30 ppm it will be difficult to maintain a chlorine level, because any chlorine added to your swimming pool will quickly evaporate and burn off in direct sunlight. If the Stabilizer level tests above 50 ppm it will also be difficult to maintain a chlorine level. Rather than partially surrounding the chlorine in your pool water to protect the chlorine, too much stabilizer will completely surround the chlorine making it inactive. In this state the chlorine is unable to combine with bacteria and harmful contaminants to sanitize your swimming pool.
Stabilizer can be added to a swimming pool if necessary to raise the level, however once Stabilizer is present in pool water it cannot be easily removed. To reduce the amount of Stabilizer in a swimming pool the water must be diluted by partially draining the pool and re-filling with fresh water. 25% of the pool water should be drained and replaced with fresh water. The pool should be circulated for 12-24 hours, and the Stabilizer level should be tested again. This process should be repeated until the Stabilizer level is within range.
The chlorine tablets and granular chlorine used to sanitize a swimming pool on a daily basis is a pre-stabilized form of chlorine. This means that the chlorine contains a small amount of stabilizer, and as chlorine is added to the pool a very small amount of Stabilizer is also added to help maintain the level. This small amount of Stabilizer constantly added with pool chlorine does not cause a problem in outdoor swimming pools because water is splashed out or evaporates, and gets replaced with fresh water to dilute the Stabilizer. This pre-stabilized form of chlorine cannot be used in indoor swimming pools, because much less water evaporation occurs and the stabilizer level will slowly buildup. Indoor swimming pool owners need to use an un-stabilized form of chlorine.
The calcium hardness of swimming pool water refers to the amount of the mineral calcium present in the pool water. The calcium hardness should be maintained at 80-150 ppm in a pool with a vinyl liner, or 150-200 ppm in a concrete or plaster finish pool. Low levels of calcium hardness can lead to corrosive water conditions, which may damage the pool surface, pool equipment and pool plumbing. If the water in a plaster or masonry finish pool becomes corrosive, the water will absorb calcium from the pool walls and floor by eating away at the pool surface until the hardness level nears 150 ppm. The calcium hardness level can be easily raised using a Calcium Hardness Increaser available from most pool supply dealers.
High levels of calcium hardness may lead to cloudy pool water and “scaling”. Scaling is most visible around the water line of a swimming pool as a white chalky deposit, but also forms inside pool equipment and pool plumbing. A pool Calcium Hardness Reducer chemical is available from most pool supply companies to lower the hardness to the desired range for your pool. You may also partially drain and refill a swimming pool with fresh water, which has a lower concentration of Calcium.
Calcium is present in the water used to fill the pool and in the pool chemicals used to treat the water. The pool chemical that adds the most calcium to pool water is standard chlorine pool shock. If you find that your calcium hardness level is too high, read the label of the pool shock you’ve been using and you will likely find that the active ingredient is calcium hypochlorite. Each time this pool shock is added to the pool water, calcium is added to the water. To prevent this problem begin using Chlorine-Free Pool Shock on a regular basis, instead of standard chlorine pool shock (Calcium Hypochlorite). The active ingredient in chlorine-free pool shock is Potassium Monopersulfate, which does the same job of oxidizing bacteria and harmful organics but does not contain any calcium. If you choose to switch to chlorine-free shock you should always still keep the standard chlorine pool shock on hand, because it is the only pool chemical capable of killing algae.
Please visit www.InTheSwim.com for a complete selection of quality pool chemicals and swimming pool supplies.
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