Chlorine Lock

• Chlorine lock is a condition of swimming pool water that results in a milky appearance. The condition is caused by high amounts of stabilizer in the pool. Stabilizers like cyanuric acid in amounts greater than 80 parts per million can cause the chlorine to work ineffectively, leading to the condition. The best way to deal with this problem is to drain part of the water out of the pool and add fresh water to the pool and continue testing it until the level of stabilizer is within the appropriate range. Using calcium hypochlorite, an unstabilized chlorine product, can help prevent buildup of the cyanuric acid.
  
  

Chemical Overdose

• Sometimes, fixing one problem in your pool can lead to an entirely different one. If you add too much calcium hypochlorite to a pool, it will also cause the water to be cloudy. While some people begin using this sanitizing product without a stabilizer to prevent chlorine lock, they find that using too much will give the same results. But the cloudy water appears for a different reason. If the pool has a scaling tendency because of high calcium hardness of the water, the pool could become cloudy with the introduction of more calcium through the sanitizer. Ideally, you should aim to keep the pool's calcium hardness between 200 and 400 parts per million.
  
  

Pool Pollution

• If your pool gets a lot of use, or it is in a place where there is a lot of dust or pollen in the air, then the pool is likely to get a little cloudy from pollution. Everything from dust in the wind to pollen to suntan lotion and sweat can pollute the pool and affect the clarity of the water. To rid the pool of these impurities, you can use a clarifier product. These pool products work as a coagulant for tiny particles in the pool, causing them to clump together in the water, making it easier for the pool filter to do its job.
  
  

Filtration Problems

• Sometimes, the cloudy water in your pool is because of ineffective filtering. Pools typically use sand, diatomaceous earth or cartridge filters to screen out the impurities in the water before sending it back into the swimming area. If the filter medium gets dirty, it may not be able to remove everything from the water. This can cause clouding. Also, if the filter medium is damaged or worn out, it reduces the filter's effectiveness at removing the smallest particles. This can also lead to cloudy water. Backwashing a dirty filter will often take care of the former problem, but a worn-out filter medium requires replacement.