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Pool Water Chemistry 101: What You Need To Know

Maintaining the water in your pool is essential if you want to get the most enjoyment out of it. Besides ensuring an enjoyable experience, properly balanced water will also optimize the performance of your mechanical equipment. Neglecting the water in your pool can cause a myriad of problems, including foul smells, high levels of bacteria, fungi, or viruses and even costly corrosion of pool accessories and filtration equipment. Fortunately, keeping the water in your pool clean and balanced is not difficult. Pool maintenance involves looking at several important elements. These include:

  • Free Chlorine – chlorine levels must be replenished to kill germs and sanitize the water

  • pH- maintaining a proper balance of acidity and alkalinity in the pool is crucial to prolonging equipment life and protecting those who use the pool from irritants

  • Cyanuric Acid –cyanuric acid is a stabilizer that protects chlorine from degradation from the sun

  • Calcium Hardness – the calcium level in your pool water must be kept high enough that calcium does not leach from the pool materials

  • Salt – many homeowners opt for a salt water chlorine generator which requires replenishment

Pool dealers sell water testing kits that will help you monitor all of these elements, and often times much more. All that is involved is sampling the water and putting it through a simple test. The results take mere minutes.

Free Chlorine

Free chlorine is the measurement of the disinfecting chlorine that is available in the water. Free chlorine should be tested daily and the chlorine level adjusted. There are automatic feeders available that allow you to test less frequently. They disperse precise amounts of chlorine into your pool water automatically. If a feeder is adjusted properly, you may not have to worry about your chlorine level for a week or more. Free chlorine degrades from sunlight. It also diminishes over time as it breaks down organic material in the water. There are charts available to help you determine just how much chlorine is appropriate for your pool based on usage and how much stabilizer you use in the water. There are countless products on the market, but buying the cheapest is not always the best idea as many of the low priced products are full of binders and fillers.Cheap chlorine tablets or sticks will crumble and fall apart in a few days, while a quality product will dissolve slowly and maintain its shape. Inorganic chlorine, like calcium hypochlorite, is a little less convenient because it must be pre-dissolved in a bucket of water before adding to it to the pool. Chlorine levels can also be raised by using a salt water chlorine generator. If the level of free chlorine drops, you are susceptible to algae in the pool. If there is no free chlorine in the pool, or algae already bloomed in the water, the pool is no longer considered safe to swim in.

pH - Acidity/Alkalinity

instatest-small_xlPool water must be tested to make sure that the level of acidity in the pool is safe for swimmers. A pH level of 7.7 and 7.8 is perfect, but anything between 7.2 and 8.0 is acceptable for swimming. If the pH level in your pools drops below this level your eyes will sting. If the level falls below 6.8, pool heaters with copper heat exchange coils will start to corrode. High pH levels can be just as destructive as they promote calcium scaling. pH levels are easily adjusted by adding muriatic acid to lower the pH, and borax to raise it.

Calcium Hardness

Calcium hardness must be maintained to prevent leaching from the plaster, concrete or other materials that come into contact with the water. The water must be saturated with calcium to prevent the deterioration of plaster. It also helps fiberglass pools resist staining and cobalt spotting. You increase calcium hardness with calcium chloride dihydrate, sold at reputable pool supply stores.

Cyanuric Acid

Cyanuric acid, often referred to as water stabilizer or conditioner, protects chlorine from the sun. Unfortunately, it also lessens the strength of the chlorine in the process. When you treat your pool water, you need to take into account how much chlorine and how much cyanuric acid is being used. Of course, the more cyanuric acid you use the more chlorine you will need to compensate for the stabilizer’s effect. Once again, there are charts to follow to determine just how much of each you will need. Cyanuric acid is available as a solid and as a liquid, but the liquid works quickly and is recommended. Be careful that you follow instructions as lowering the level of cyanuric acid requires either water replacement or a reverse osmosis water treatment.


peedps_shock_2kgSalt is only a concern if you opt for a salt water generator. The proper salt level will be outlined in your manual. It is generally sold in bags and it should be 99.4% pure to avoid additives. Pool store salt is slightly more expensive than the salt used in water softeners as it is ground more finely. It is also recommended that you “shock” your pool weekly. Chlorine loses its potency over time, but it can also bind with other substances that can irritate the skin. Shocking the pool is actually super-chlorinating it. By adding three to five times the normal amount of chlorine or other chemical sanitizer to the pool water, bacteria and other organic matter are killed and free chlorine is boosted. Many also recommend adding a dose of algaecide to combat algae bloom. Maintaining your pool need not be an ordeal. A simply pool testing kit and regular water adjustments will ensure that you pool is perfectly suited to swimming, and your equipment will love you for it too.

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