Swimming Pool Blog

How to Clear Up Cloudy Pool Water

Turbid water conditions create safety hazards
by Rob Cox
, July 28, 2011

Get Your Swimming Pool Out of the Cloud

cloudy pool waterCloudy pool water has caused quite a stir lately. Last month in Boston (June 26, 2011), a young woman laid at the bottom of a Boston swimming pool for two days, until some late night fence-jumping teenagers discovered her body floating in the pool.

Lifeguards on the scene closed the deep end of the pool for safety reasons just minutes after the drowning, unaware that the unsafe water condition had already claimed a life.

Cloudy or turbid pool water can present a number of unhealthy issues. Cloudy water is unsafe for diving because you can't see the bottom, unsafe for swimmers because lifeguards can't see the bottom, and the water is likely unsanitary, as well.

Cloudy pool water usually indicates insufficient filtering and/or insufficient sanitizer. Swimming in cloudy water could mean an increased risk from waterborne pathogens such as E. coli and Pseudomonas, or the chlorine-resistant protozoan known as Cryptosporidium, or "Crypto" for short.

How to Prevent Cloudy Pool Water:

  1. Maintain proper water balance. Chlorine and pH levels should be maintained at 1.0-3.0 ppm and 7.4-7.8, respectively.
  2. Proper levels of calcium hardness and total alkalinity help to prevent solids from precipitating out of solution.
  3. Pool pumps should run long enough daily to filter all of the water at least once - maybe even twice during warmer months.
  4. Shower before swimming. Cosmetics, hair and skin lotions, deodorants, etc. all contribute to cloudy pool water.
  5. Superchlorinate the pool at the first sight of hazy water conditions, before it turns cloudy and then murky.
  6. Keep a level of cyanuric acid in the pool water, at a minimum of 40 ppm, to help reduce the summer sun's effect on chlorine levels.

How to Correct Cloudy Pool Water:

  1. Clean pool thoroughly to remove all organic debris.
  2. Balance the pool water. If your test kit is old or untrustworthy, take a sample to a local pool store for testing.
  3. Run the filter 24/7 until clear. Don't backwash or clean filters until the pressure guage is 8-10 PSI higher than the clean or starting pressure. Added dirt in a pool filter will aid in trapping even smaller particulate matter.
  4. Shock the pool with up to 3 pounds of granular chlorine per 10,000 gallons of water. If chlorine does not register afterwards, you may have an abnormally high level of cyanuric acid in the pool. If over 100 ppm, lower CYA level in water by dilution. Drain out 20% of pool, then refill.
  5. Use a pool clarifier, which acts as a coagulant for very small particles. Don't overdose, and follow label instructions carefully.
  6. Make sure that your pump is operating at peak power by cleaning pump baskets and sealing any air leaks.
  7. If small particles are passing through your filter while vacuuming, set multiport valves to the waste position while vacuuming.

If Your Cloudy Pool Water Just Won't Seem to Correct:

  1. Consider the possibility that your filter is undersized or the filter media (sand, cartridge, grids) will need to be replaced. 
  2. If you have a diatomaceous earth (DE) pool filter, dissassemble and clean thoroughly, and inspect the grids for tears or damage.
  3. Is the filter pressure normal? If the PSI is much lower than normal, the pump impeller, pump basket or pipes could be clogged.
  4. Water could be bypassing the filter from a faulty backwash valve. Again, look for lower than normal filter pressure.
  5. Is your pump operating correctly? Make sure it's not overheating and cycling on and off.
  6. Are there external sources of heavy dust, pollen or mudslides entering the pool when you're not looking? This could be one source of your water clarity issues.

In extreme cases where I just can't seem to clear the pool, no matter what I do, I like to use a flocculent and "floc" the pool. There are many commercially available pool flocculents, or you can use alum. Also known by it's label name, aluminum sulfate can be a very effective flocculent, but leaves a jelly-like substance on the pool floor, which must be slowly vacuumed to waste.

To use alum in a pool, first balance the water chemistry, with pH on the high side (7.8). Clean all debris from the pool floor and surface. Broadcast over the surface: use 4 pounds of Alum per 10,000 gallons of pool water, followed by an immediate treatment of 2 pounds of shock per 10,000 gallons. Shut the pump off and keep it off overnight. Vacuum to waste the floc on the floor of the pool.

Keep your swimming pools clean and clear this year! Cloudy pool water proves itself over and over again to be dangerous to swimmers and divers. If you cannot see the bottom of the pool, close the pool immediately, and do not allow use until you can clear up the pool water.