No owner of a chlorinated swimming pool welcomes the need to superchlorinate, or shock, her pool after it's been contaminated, usually by algae. Fortunately, a properly carried out pool shock will disinfect a pool fully. However, there are instances in which a shocked pool then develops cloudy water. High pool chlorine levels after shocking, though, aren't the reason for cloudy water. Rather, a pool that's cloudy once it's been shocked is suffering from the presence of dead algae and debris.
It's recommended that swimming pool owners shock their pools at least weekly or after they've been contaminated by algae or other debris. Shocking a pool involves raising its chlorine levels to 10 to 25 parts per million (ppm). The more contaminated a swimming pool is, the higher you should raise chlorine levels during shock treatment. Shock treatment of a pool doesn't itself cause cloudy water, though. In fact, shock treatment eventually produces clearer pool water, though it sometimes leaves behind dead matter.
Shock treated pools that turn cloudy are displaying a film of dead or dying algae or debris on underwater surfaces, which is known as biofilm. Swimming pool biofilm is killed by additional chlorine shocking. Once a pool biofilm is completely killed by additional chlorine shocking, the pool's water will begin clearing up. To completely clear away killed biofilm in a swimming pool, just add clarifier. Pool clarifiers work by binding with particulate matter in the water so that it can be filtered out.
There are times after a swimming pool is shocked when its water will turn milky, which can be confused with cloudiness. Milky water in a pool sometimes occurs after the pool has been shocked with calcium hypochlorite chlorine and its water has high calcium hardness levels. High calcium hardness levels in a pool are a sign that the pool's water is too hard. If calcium hardness levels are above 200 ppm and calcium hypochlorite is always being added, milky looking water sometimes results.
Preventing cloudy or milky looking water in a swimming pool is best accomplished by maintaining consistent chlorine and pH levels, to start. Pool chlorine levels should be between 1 and 3 ppm. Also, keep pool pH between 7.2 and 7.8 so that chlorine will work efficiently and prevent pool contamination in the first place. Use either a calcium sequestering additive to eliminate milky pool water or switch from solid calcium hypochlorite chlorine to sodium hypochlorite liquid chlorine or other alternative forms.
For outdoor pools with cloudy water, a special cause of cloudiness may be too much cyanuric acid (CYA) chlorine stabiliser in the water. CYA in a pool helps protect available chlorine from being too quickly dissipated by the sun's rays. However, an excess of CYA in a pool will greatly slow down chlorine effectiveness and lead to cloudy water in many cases. Maintain CYA levels in a chlorinated pool between 30 and 80 ppm.