In a typical residential pool, the chlorine loss to sunlight even with CYA and low swimmer loads is about 1.5 ppm per day or about 10 ppm of chlorine per week. This means that if you started with a low CYA of only 30 ppm, in about three weeks you would be at 50 ppm. This is the maximum CYA that we recommend.
As for normal chlorine demand, it varies by pool, but is usually somewhere between 1.5 and 3 ppm FC per day with most having around 2-2.5 ppm FC per day. This assumes that the FC starts out at around 10% of the CYA level and that the CYA level is high enough to protect the pool in sunlight.
A standard 8 x 4 pool (50,000 ltrs) will require 250 grams of chlorine per day. (not considering other factors like chlorine consumption). On the filtration side of things, remember that filtration relies on both the circulation of the water and filtration equipment.
Natural dechlorination will occur over time and chlorine will dissipate when exposed to the air and sunlight. This process can take 5-10 days, depending on a variety of factors, including pool size.
Under normal conditions, you should add a chlorine tablet every 3-7 days. However, several factors can influence how often you need to add chlorine: Frequency of use: A heavily used pool will require more frequent chlorination. Sunlight: Sunlight breaks down chlorine, so you'll need to add it more often on sunny days.
The consistent inability to maintain chlorine levels is also called “chlorine demand” and is most often 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 reading at all it may be due to very high chlorine demand. 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.
Direct sunlight (UV)
Direct sunlight breaks down chlorine. Without a stabilizer (cyanuric acid) in the water, as much as 90% of free available chlorine could be destroyed within just two or three hours.
In most cases, it takes 24-48 hours for chlorine concentration to drop significantly. If the water is too hot or the chlorine levels are too high, it may take longer for the chlorine to evaporate. You can speed up the process using a chemical oxidizing agent or diluting the water with fresh water.
There are three main ways to remove chlorine from tap water. Leave it to stand in the open air for up to 24 hours, boil the water, or install a drinking water filter or whole house water filter that contains a carbon block water filter cartridge.
Chlorine can irritate the eyes, skin, hair, and teeth. Swimming occasionally doesn't cause significant side effects. People who swim frequently are more likely to experience chlorine side effects. Chlorinated water is considered safe when pools have the correct concentration of chlorine.
Typically, you will need to add chlorine tabs or granules to your pool on a constant basis. About every two weeks, you will need to shock your pool with a higher dose of chlorine. This raises the pH levels quickly and is especially important in sunny weather when the chlorine can break down.
For the pool owner who wants that instant gratification, liquid chlorine may be the best way to get you back into your pool. But for the pool owner who regularly uses the pool and wants the convenience of not having to perform as much maintenance, tablets may be preferable.
6. Pool Is Losing 1 Inch of Water Per Day. Losing more than ½” of pool water per day indicates you likely have a leak in your pool's structure or your pool pump system. You should call your pool service for a thorough leak inspection.
More water in the pool = lower concentration of chlorine in the pool. Rainwater also lowers chlorine by collecting pollutants, particles, and other contaminants in the air on its way down and delivering them into the pool or spa water.
Water in a pool without chlorine can start to become unsafe in as little as 24 to 48 hours.
Bacteria, algae and microscopic contaminants, such as urine, sweat, sunscreen and beauty products, take a toll on your swimming pool's water chemistry. These substances, when present in your pool water, accelerate chlorine demand and can affect your chlorine's ability to maintain properly sanitized water.
Regardless of how frequently or what system you use to add chlorine to the water, the chlorine level should stay between 1.0 and 3.0 parts per million (ppm) to maintain a healthy pool.
Shock is chlorine, in a high dose, meant to shock your pool and raise the chlorine level quickly. Chlorine tabs (placed in a chlorinator, floater, or skimmer basket) maintain a chlorine residual in the water. You do need to use both tabs and shock.
The sun's UV rays break down the chlorine, and it is released into the atmosphere. In summer, when the sun is bearing down, it'll only take around two hours for 90% of the chlorine in your pool to be broken down completely.
For my pool with a mostly opaque cover the chlorine loss rate at 50ºF is roughly 1 ppm FC every 14 days or around 1.7% loss per day. One would get from a shock level that is a 40% FC/CYA ratio down to a regular 7.5% FC/CYA ratio after (1-1.7/100%) days = 7.5/40 gives us 98 days or a little over 3 months.
Exposure to over-chlorinated water can provoke eye and skin irritation, lung irritation, and asthma. In addition to being bad for your health, the excess-chlorinated pool can eventually become dangerous. High chlorine levels tend to lower the pH level of the water, making it more acidic.
Surely it's safe to swim in. FALSE. It doesn't matter how much time and effort you put into skimming, brushing, vacuuming, circulating, and filtering your pool. If there's not enough chlorine in the water, your pool's not actually clean, and the water's not safe.
Use a chlorine shock
Low levels of chlorine can be a common reason for cloudiness in your pool, so it's a great idea to shock the water to elevate the chlorine levels. This will sanitize the water and clear any buildup of contaminants.
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.