In short, the UV rays produced by the sun have a major effect on chlorine. When exposed to UV rays, chlorine ions begin to separate, which eventually destroys them. And as your chlorine burns away, your sanitizer level drops. This is the very reason why CYA (cyanuric acid), or chlorine stabilizer, exists.
Maintain Proper pH Levels
Your pH levels affect your chlorine levels and the ability for the chlorine to do its work properly. If your water's pH is too high, it hinders the chlorine's ability to efficiently clean the pool. A water pH level that is too low causes the chlorine to dissipate more quickly.
What is Chlorine Loss? Chlorine demand is the consistent inability of your pool to maintain chlorine levels. It's usually caused by a high level of inorganic and organic contaminants in the water. Those contaminants force the chlorine to work extremely hard to oxidize them, leaving little chlorine to protect swimmers.
If you test your pool water and can't get a chlorine level reading at all it may be due to a very high chlorine demand. A high chlorine demand is the inability to keep an adequate level of chlorine in the pool water even though the water appears to be balanced and properly maintained.
Warmer air will cause the chlorine to evaporate more rapidly. If you decide to place the water in a jug that's left open in the refrigerator, the chlorine should evaporate completely within 24 hours. For quicker evaporation times, leave the water at room temperature.
The only way to cure chlorine demand is to give your pool the chlorine that it needs through consistently shock treatments. A general rule to follow is to use 3 pounds of calcium hypochlorite pool shock for every 10,000 gallons of pool water. This may vary depending on the degree of chlorine demand that your pool has.
Warmer air will cause the chlorine to evaporate more rapidly. If you decide to place the water in a jug that's left open in the refrigerator, the chlorine should evaporate completely within 24 hours. For quicker evaporation times, leave the water at room temperature.
Total chlorine is simply the combination of free and combined chlorine. Shocking then releases the combined chlorine and off-gasses the contaminants, increasing the amount of free chlorine in your pool or spa.
When you're shocking a pool, the goal is to raise the free chlorine level of the pool water to roughly 10 times the combined chlorine level.
The addition of a cyanuric acid stabilizer to pool waters treated with chlorine is necessary to protect the active life of chlorine and its derivatives in the waters from the damaging effects of the sun's ultraviolet (UV) rays. When exposed to UV rays, chlorine evaporates rapidly.
The Bottom Line about Pools and Chlorine
As mentioned above, you could probably swim in a pool without chlorine without any major health issues. However, long-term use of a pool lacking chlorinated H2O could make you sick or, at the very least, contribute to rashes and other types of skin irritation.
Shock is liquid or granular chlorine. You should add one gallon (or one pound) of shock per 10,000 gallons of pool water every week to two weeks. During hot weather or frequent use, you may need to shock more frequently.
Low levels of chlorine or bromine may not be able to kill algae spores, resulting in algae blooms and cloudy pool water.
After Shocking Your Pool
It is safe to swim once your chlorine levels are around 5 ppm or after 24 hours.
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.
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.
As little as two hours of sun exposure — that's all it takes to reduce chlorine content by 90%. That's because ultraviolet light is a type of electromagnetic radiation. This, in turn, makes it powerful enough to split apart chemical bonds. In pool chlorine, UV light breaks the bond of the substance's hypochlorite ions.
The ultraviolet rays of the sun can reduce chlorine by up to 90 percent in two hours! And if it's a hot day, warmer water tends to breed more bacteria, and so the pool's chlorine gets used up faster and must be replenished more frequently.
How Long Does It Take for Chlorine to Evaporate Out of Water? Water needs to sit for a minimum of 24 hours to dechlorinate. It can actually take almost 5 days for chlorine to evaporate completely from the water, depending on the initial concentration of the chlorine, and the total volume of water.
A chlorine level of between 3-5mg/l must be maintained in your hot tub at all times. The addition of chlorine will depend upon usage and bathing habits. It could be daily or every 2-3 days (for 1mg/l add 2g per 1000 litres).
Daily as needed and indicated by measurement. One caveat, however: if your total alkalinity and pH are not where they should be, you will find it difficult to keep enough free chlorine in your pool water. Adjust your alkalinity first, then correct your chlorine.
Therefore, you should be testing your pool water's chlorine and pH levels every two weeks. Maintaining proper water chemistry will reduce the amount of work needed when you're ready to start swimming again.
Strong Smell of Chlorine
A healthy, safe pool will have little to no odor. That smell comes when your pool is out of balance. The smell of chlorine arises when the chemicals are dealing with a lot organic material like sweat, urine, and bacteria in your pool.