Free chlorine involves the amount of chlorine that's able to sanitize contaminants, while combined chlorine refers to chlorine that has combined directly with the contaminants. Total chlorine is basically the sum of free chlorine and combined chlorine.
The sum of combined chlorine and free chlorine is total chlorine (combined chlorine + free chlorine = total chlorine). Inexpensive chlorine tests typically show total chlorine only. Since clean chlorinated water contains no combined chlorine, total chlorine in a sanitized pool is the same as free chlorine.
Raising pool chlorine can be much easier than trying to lower chlorine levels. Simply adding chlorine in the form of chlorine tablets, granular chlorine, liquid shock or powder shock will increase the total amount of chlorine within the pool.
It takes 25 parts of Combined Chlorine to do the work of one part of Free Chlorine. If the Total Chlorine in your pool is higher than the Free Chlorine reading, then the difference between the two represents the level of Combined Chlorine in the water. If the readings are the same, then no Combined Chlorine is present.
For a healthy pool, the free chlorine level should be between 1.0 and 3.0 parts per million (ppm). The Centers for Disease Prevention and Control recommends pH 7.2–7.8 for pools and hot tubs.
Free chlorine is just that, free. Free to interact with other chemicals, algae, bacteria or the like. ... Shocking then releases the combined chlorine and off-gasses the contaminants, increasing the amount of free chlorine in your pool or spa.
Pools will naturally gas-off chlorine from the surface, and very high levels can irritate airways and lungs. This is especially true for indoor pools. At chlorine levels over 10 ppm, swimsuits can begin to fade. Pool covers become damaged, and the water is generally uncomfortable and unsafe for swimmers.
Free chlorine refers to the amount of chlorine that has yet to combine with chlorinated water to effectively sanitize contaminants, which means that this chlorine is free to get rid of harmful microorganisms in the water of your swimming pool.
We're probably all familiar with at least one of the common side-effects of swimming: sore eyes, skin irritations, fading swimming costumes, and that lovely smell that lingers until you've had a good shower. But chlorine itself, when used at the recommended low levels, is perfectly safe.
Simply dip one test strip into pool or spa water at elbow's depth and remove immediately. Shake once to remove excess water. Hold strip level and visually compare the strip to the color chart included on the bottle. Select the corresponding test result colors within 15 seconds of wetting.
Exposure to high levels of chlorine can cause lung irritation, skin and eye damage, and provoke asthma. Not only is it bad for your health, but it can be bad for your pool due to the increase in chlorine. High chlorine levels decrease the pH of your pool's water, making it more acidic.
Reasons it could be high:
Your pool has been over dosed with too much liquid or powder chlorine. Your Chlorinator is turned up too high. Your TOTAL chlorine level is high (and your FREE chlorine is low) but ineffective due to a “chlorine lock”, which happens when too much Cyanuric Acid is added to the pool.
No matter what type of chlorine system you choose to use for your pool, remember that the chlorine level should remain between 1.0 and 3.0 parts per million (ppm) to ensure a safe and healthy pool. If the levels are any higher, you may be at risk of swimmer's itch and red eyes.
Liquid chlorine and granular shock have the same active chemical that sanitizes your pool, what changes is the strength and the way you use it. Liquid chlorine is less costly, unstabilized and comes in liquid form. Granular shock is stabilized and comes in a solid form that dissolves in your pool.
A pool filter should be run for a minimum of 6 hours after shocking a swimming pool. This is to allow the filter to clean the water and give the shock enough time to fully mix with the pool water. Running the filter after shocking for 24 hours to 7 days is necessary if the pool has a large amount of algae.
The best time of day to shock your pool is in the evening. This is because the sun's rays can affect the effectiveness of the chlorine by dissolving it too quickly, before it has a chance to rid the pool of contaminants and clean the water.
You Notice Signs of Eye or Skin Irritation
If you or your family members start experiencing signs of irritation during or after you swim in the pool, there may be too much chlorine present. You could notice that your eyes are itchy, red and watery, or you might notice that your skin is very dry, very itchy or very red.
7. Using liquid chlorine raises the pH of the water. Liquid chlorine does not raise pH. When added to water, liquid chlorine (which has a pH of 13) makes HOCl (hypochlorous acid – the killing form of chlorine) and NaOH (sodium hydroxide), which raises pH.
Of course, too much chlorine in pool water can be dangerous. Exposure to over-chlorination can provoke asthma, lung irritation, and potentially skin and eye irritation. As well as being potentially bad for you, it's bad for your pool.
At temperatures above 78 to 82 degrees Fahrenheit, chlorine dissipates faster, algae grows better, and the formation of scale (calcium carbonate deposits) is more likely to occur. There are no State laws regulating swimming pool temperature, but spa temperature may not exceed 104 degrees Fahrenheit.
The Mayo Clinic finds that the most comfortable pool temperature range is between 83°F and 88°F. Pools used for physical therapy must also be at a higher temperature, ideally around 86°F. Warmer temperatures also benefit those who swim to relax muscles or to make stretching exercises easier.
As I previously mentioned in my list of pool care essentials, having a thermometer to track your pool temperature is important because algae loves to grow in hotter temperatures––generally 85 degrees or above.
At lower temperatures chlorine lasts far longer than it does at higher temperatures, so you will probably only need to add chlorine once every week or two. Note: most SWGs shut down around 50 degrees, so you can't usually depend on a SWG to maintain the FC level over the winter.
When the levels are properly balanced, chlorine will keep the algae at bay, but the water will slowly begin to turn green as the algae take over if there's not enough. But be careful—adding too much chlorine in pool water can cause those metals to oxidize and turn the pool a different shade of green.