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Cloudy Pool Water — What Causes It and How to Correct It

Cloudy water in a pool

It’s something that no pool owner wants to see when they head out for a refreshing dip on a hot summer day — cloudy water. While that milky or hazy look signals some sort of imbalance in the water, exactly what the issue is requires some investigation. With that in mind, here’s a breakdown of the various causes of cloudy water and how to correct these issues.

Lack of Free Chlorine

When measuring chlorine levels in a pool, it’s important to take note of the free chlorine levels in the water. The free chlorine is chlorine that has not yet been used up and is still available to sanitize the water. The total chlorine numbers don’t give an accurate picture of the sanitizing capabilities of the water as they show the total amount of chlorine in the pool, even though much of that chlorine may already be combined with contaminants and is, therefore, unavailable.

Having lower than acceptable levels of free chlorine is the most common cause of cloudy pool water. Low free chlorine is an issue that needs to be attended to right away so that algae and ammonia levels don’t have a chance to overtake the water.

Outside of test results, a good indication that cloudy water is caused by low free chlorine is the smell of the pool water. Combined chlorine (chlorine that is already mixed with ammonia or nitrogen compounds and is now unavailable for sanitizing) has that distinctive smell that is so often associated with swimming pools. While many people assume that the smell indicates that a pool contains a lot of sanitizer, the truth is that it’s actually indicative of sanitizer that is used up.

Testing for Free Chlorine

chlorine testing for cloudy water

You want your free chlorine levels to be at 3 ppm (parts per million) and your combined chlorine reading to be under .5 ppm. If free chlorine is below 3 ppm and combined chlorine is above .5 ppm, it’s time to shock the pool. Shocking adds a large dose of chlorine to the pool all at once to get free chlorine levels back up fast. Even saltwater pools that have become low on free chlorine may require a dose of regular chlorine shock to get back on track.

High Ammonia

If cloudy water is not cleared easily by shocking the pool and the levels of free chlorine and cyanuric acid are reading at around 0 ppm, despite the addition of the extra chlorine, there is a good chance that there is ammonia in the water. In such instances, combined chlorine will also be reading high (above .5 ppm).

pH and cyanuric acid testing for cloudy water

If a pool has ammonia issues, it takes very large doses of chlorine to regain balance. Typically, multiplying the amount of ammonia by 10 will give an indication of the amount of free chlorine required to regain balance. This means that if there is 10 ppm of ammonia in the water, free chlorine will need to be taken up to about 100 ppm to overtake the ammonia. 

High ammonia is not a common issue, but occurs more often at the beginning of the warm season. Ammonia uses up chlorine faster than anything else, so it’s important to be aware of the potential issue. It’s significant to note though that a CYA reading of 0 does not necessarily mean that ammonia is present.    

Early Algae Growth

Algae that has not yet shown up as visible growth in your pool can appear as cloudy water. Taking care of an algae issue when it’s in the early stages is the best course of action so that it doesn’t turn into a full algae bloom. A common time to find cloudy water due to early algae growth is as the weather is beginning to warm up in the spring. 

When algae is causing the cloudy water issue, the water will often have a slight green, yellow, or dark look. The pH of the water is also likely to be off and free chlorine will likely be depleting quickly. To test you may perform an overnight chlorine loss test (OCLT). 

Performing an OCLT Test

  • After sundown, add chlorine to the water and test the free chlorine levels.
  • Check the free chlorine levels again first thing in the morning (before the sun begins to heat up the pool, leading to chlorine loss).
  • If the levels of free chlorine have gone down by more than 1 ppm, then algae is likely causing the cloudy water problem.

If algae is the cause of cloudy pool water, then there are several steps to take immediately. Start by thoroughly brushing the pool’s surfaces to loosen the algae. After brushing, you may want to add a pool flocculant, which causes small particles to gather together and sink to the bottom of the pool. Next, set your pool vacuum to “waste” and vacuum out the debris. Then, balance the water. Shock the pool and finally, add algaecide or use a product that combines both.

 

shock and algaecide for cloudy water 

 

While clearing algae is certainly not impossible, especially when the issue is in the early stages, it can be a frustrating process. The best idea is to prevent algae from the start. Adding a PoolRX™ unit is a simple and effective method for keeping algae at bay. A PoolRX unit sits in the skimmer basket or pump basket and prevents algae for up to six months at a time. 

PoolRX for killing algae

Pool RX also makes a booster product to extend the life of a PoolRX unit or for additional help with clearing existing algae and cloudy pool water issues.

Filter or Pump Issues

Issues with the filter or pump can also be to blame for cloudy pool water. Here are a few things to check for:

  • Dirty or damaged filter -If the pool filter is either too clogged up or too damaged to properly pull particles from the water, cloudiness can occur. Cleaning and inspecting the pool filter regularly will help to avoid these issues. If the water is cloudy, be sure to check the condition of the filter.
  • Pump not running often enough – The pool pump should turn over the entire water volume at least once in a 24-hour period. If the water isn’t moving at least this much, it won’t get filtered properly and organisms will begin to grow.
  • Pump is not functioning properly – if a pool pump is not operating as it should, the water cannot circulate and be filtered as it needs to be. Some common signs of pump issues are: consistently low PSI readings (under 12 PSI) on the filter, water leaking from the pump, and screeching, grinding, humming, or popping sounds coming from the pump motor.

 

At Alpha West, we work with only the best in pool and spa manufacturing. If you want to learn more about what we do and the products we represent, get in touch with our knowledgeable team of pool and spa manufacturer reps at hello@alphawest.com.

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