Cyanuric Acid (Stabilizer)
The sun’s ultraviolet (UV) rays will make the chlorine in an outdoor pool dissipate quickly. In fact, an ideal level of chlorine in an “unstabilized” pool or spa can be lost in less than two hours on a bright sunny day, due to the UV rays of the sun. Cyanuric acid acts as a “stabilizer” that helps chlorine hold up better when exposed to the UV rays. You can think of cyanuric acid as blocking the effect that the sunlight has on breaking down the chlorine—kind of like a sunscreen for your pool.
You should maintain an ideal level of cyanuric acid, 30 to 50 ppm (mg/L), to prevent rapid chlorine loss. If the cyanuric acid level is too low, you may need to add more to the water. However, be advised that cyanuric acid will make the pH of the water lower (more acidic), so you may have to adjust the pH upward as well.
On the other hand, too much cyanuric acid will reduce the beneficial effect of your chlorine, leading to stains or cloudy water. Some chlorine compounds already contain an amount of cyanuric acid. If you are using dichlor or trichlor as your primary chlorine sanitizer, you are already introducing cyanuric acid along with the chlorine. If the cyanuric acid level is your pool or spa is too high, you will need to partially drain and refill with fresh water.
When you first fill your pool or spa, test the cyanuric acid level until you have added enough to reach the ideal range. After that, test cyanuric acid a minimum of once a month throughout the pool season. If you are using dichlor or trichlor, you will have to test cyanuric acid more frequently to ensure that the level has not exceeded the upper limit.
Free Chlorine
Every sanitizer has two key functions, to sanitize (kill bacteria and all living organisms) and also oxidize (destroy contaminants and waste). The most popular pool and spa sanitizer is chlorine. Chlorine is also classified as a disinfectant, meaning that it is capable of killing bacteria, algae and other organic material instantly. All chlorine does the same thing when it is added to the water, regardless of the type of chlorine added. It forms free available chlorine. Free chlorine is the form of chlorine that kills bacteria, algae and disease-causing organisms. It is the attack dog that guards your pool against microbiotic intruders. (In general, you wouldn’t want a dog in the pool, but this is an exception.)
You must maintain free chlorine at a sufficient level to disinfect potential contaminants on contact. The more chlorine in the water, the more it can sanitize and oxidize the water. (Remember that sanitizing and oxidizing are the processes that chlorine uses to keep the water clear and clean.) However, if the free chlorine level gets too high, it can make the water uncomfortable for swimmers. The trick is to keep the free chlorine level in the ideal range. In a swimming pool, keep free chlorine at a minimum of 1 ppm (parts per million) and a maximum of 10 ppm, with an ideal concentration of 1 to 3 ppm.
In spas the level needs to be maintained at a slightly higher level due to the smaller volume and higher temperature. The minimum level should be 2 ppm in a spa, again no higher than 10 ppm, and ideally 3 to 5 ppm.
Total Chlorine
Chlorine in pool and spa water may be present in two forms. It is free chlorine that does the hard work of killing bacteria and oxidizing contaminants. (When you add a chlorine compound like Cal-Hypo or trichlor to your pool, you are actually adding free chlorine.) When the free chlorine combines with these contaminants, such as oils, swimmer waste and other organic compounds, it becomes combined chlorine, or chloramines. In pool and spa water, this form of chlorine has very little sanitizing ability, and no oxidizing ability. You can think of combined chlorine as a spent bullet.
Total chlorine is just the sum of both combined chlorine and free chlorine. In other words,
(total chlorine) = (free chlorine) plus (combined chlorine)
Knowing your total chlorine and free chlorine levels allow you to calculate combined chlorine (combined chlorine = total chlorine minus free chlorine). If the total chlorine level is higher than free chlorine, it is obvious that combined chlorine is present. In that case you need to shock or superchlorinate your pool or spa. To shock the pool, you add a free chlorine compound in an extra large dose. The high dosage of free chlorine will actually oxidize (destroy, burn off) the combined chlorine.
Bromine
Bromine is a popular pool and spa sanitizer often used instead of chlorine. Bromine has some distinct differences from chlorine. One advantage is that bromine works better for spas / hot tubs (with hotter water and lower water volume) than chlorine does. On the minus side, bromine is sensitive to sunlight, deteriorating rapidly when exposed to the sun. It can also be more expensive than chlorine. For these reasons, bromine is less popular than chlorine for use in outdoor pools.
There are two forms of bromine, free and combined. Together these two are called total bromine. Both forms of bromine are sanitizers, meaning that they can kill bacteria, algae or other living organisms in the water. Be sure to use a test kit that measures total bromine, since that is the best indicator of the level of sanitizer in your water. The ideal concentration of total bromine in a swimming pool is 3 to 5 ppm. The ideal in a hot tub or spa is 4 to 6 ppm. (In spas the level should be slightly higher level due to the smaller volume and the higher temperature of the water.)
You have to monitor the bromine level continually, almost daily, as it will fluctuate constantly. Environmental conditions (leaves, rain) and usage (how many folks are enjoying the pool or spa) will add contaminants in the water. Those contaminants will decrease the bromine existing in the water. Be sure to test the bromine before entering the water. Even if the system is dormant or not in use, you should test the bromine level at least weekly to prevent any build-up of bacteria or algae.
Hardness
Water hardness occurs as an indirect side effect of various chemical compounds. Calcium and magnesium are the two primary minerals that make up hardness in water. Like alkalinity and pH, hardness affects the tendency of the water to be corrosive or scale-forming. (Scale is a deposit that forms on pool walls and equipment when the mineral content of the water is too high.) By maintaining the ideal ranges for hardness and alkalinity, you can keep scale formation to a minimum.
Low hardness levels require immediate attention! They can be very dangerous to your system. Water that is not properly saturated with hardness—water in which the hardness level is too low—will be very corrosive, causing significant damage to metal pipes and fixtures as well as plaster. You must be sure to balance hardness before adding any sanitizer to the water. Otherwise, the water will become even more aggressive (corrosive); it can cause severe damage in a short period of time.
When the hardness level is low, increase the hardness immediately to limit the damage of corrosive water. You can increase the hardness level by adding a chemical like calcium chloride. When the hardness level is too high, excessive scale formation occurs, and the water may become cloudy or discolored. Elevated pH and warmer temperatures will increase scale build-up too. If the hardness level is too high, you can partially drain and refill with fresh water.
The ideal level of hardness for your pool or spa water is from 200 – 400 ppm (mg/L). You should test hardness when adding fresh water, and re-test until you have balanced the water hardness properly. After that, test hardness a minimum of once per month throughout the season. If you use calcium hypochlorite as a sanitizer, you need to test more frequently to ensure that the level has not exceeded the upper limit.
pH
We use pH as an index to express how acidic or basic a solution is. (The scientific definition of pH is “the negative logarithm of the hydrogen ion concentration”.) A pH greater than 7.0 is basic, and a pH lower than 7.0 is acidic. In pools and spas, it is important to maintain the water in the slightly basic range of 7.2 to 7.8. The National Spa and Pool Institute (NSPI), the industry association in the United States, has set a standard of 7.2 to 7.6 as the ideal pH.
If pH Is Low:
The water can corrode surfaces, metal equipment or fixtures.
Swimmers and bathers can experience discomfort from burning eyes and itchy skin.
The chlorine may dissipate more quickly.
The water may cause pitting and etching of plaster surfaces.
If pH Is High:
Calcium and metals tend to come out of solution (the opposite of dissolving) at high pH levels, creating the potential for staining and scale formation. The calcium and metals will actually create deposits and discoloration on pool walls and equipment.
Swimmers and bathers can experience discomfort from burning eyes and itchy skin.
High pH can contribute to cloudy water.
Alkalinity
Total alkalinity is the measure of the amount of alkaline buffers (primarily carbonates and bicarbonates) in your water. These alkaline substances buffer the water against sudden changes in pH. Total alkalinity is considered the key to water balance. It is the first parameter you should balance when making routine adjustments to your water.
If you neglect to check the total alkalinity in your pool or spa, you may have trouble balancing the pH. You may also notice that pH fluctuates suddenly despite your best efforts to keep it in the ideal range. If the alkalinity is too low, anything introduced to the water will have an immediate impact on pH. Abrupt shifts in pH can cause scaling or corrosion of metal equipment and fixtures as well as other problems. When the total alkalinity is high, the pH has a tendency to drift upward, causing scale to form.
Maintaining an ideal level of alkalinity will protect your pool or spa and its equipment from the harmful effects of sudden pH fluctuations. Think of the alkalinity as training wheels: it keeps the pH in balance without allowing it to tip too far to either side. Of course the pH can still drift upward or downward, but that change will happen gradually as long as the alkalinity falls within the ideal range. The ideal range of total alkalinity for pools and spas is between 80 and 120 ppm (mg/L).
When the total alkalinity is too low, add sodium bicarbonate. If the total alkalinity is too high, you can lower it by using muriatic acid or sodium bisulfate.
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