So you’ve got your pool up and running, cleaned out all of the leaves and dirt, and everything’s looking good, then one day you look out and notice that your pool is green or cloudy. What happened? In this entry we will talk about the different causes of cloudy water, how to troubleshoot to find the exact problem, and how to get the water clear again. 

Causes and Effects of Cloudy Water

Cloudy water can be caused by several things. The most common is a lack of chlorine. If this is the case you should avoid swimming in the pool as water without chlorine isn’t being properly sanitized, and therefore can contain potentially harmful bacteria.

Another very common way that water turns cloudy is from very fine particles getting into the water. At their best, sand filters will filter down to around 20 microns. Anything finer than 20 microns will pass right through the filter and back into the pool. As these particles build up they will cause the water to look cloudy. The most common cause of this type of cloudiness is dead algae. These particles are usually harmless and the water is still safe to swim in.

Poor filtration can also be the cause of cloudiness in pool water. When new, the sand in a pool’s sand filter is full of sharp peaks and valleys. Particles are trapped in the valleys as water passes through the sand. Over time, water passing through the filter rounds out those peaks and valleys, meaning that the sand is no longer effectively trapping particulate in the pool. The paper filters in pool cartridge filters can also degrade over time, causing the same issue.

Even if your filter is brand new, you can still get issues with cloudiness if your pump isn’t running long enough. In order to properly filter the water, and keep it clear, all of the water in the pool must pass through the filter 2-3 times per day. For an average sized pool this means running the pump for 10-12 hours a day. Cloudiness from poor filtration is again harmless, as long as there is a chlorine residual in the pool water.

Excessively high pH, alkalinity, and/or calcium hardness can also cause cloudiness issues. Acidic water can hold more particulate in suspension than water that is basic. So, the higher the water’s pH, the less stuff (like calcium) it can hold in suspension. When water that has a lot of dissolved solids in it, increases it’s pH/alkalinity, those solids can “fall out” of the water, making it look cloudy. These particles are harmless to you, but can cause scaling on the pool surface, or plumbing, if left untreated. 

Troubleshooting Cloudy Water

As with any water related problem, you should get your water professionally tested anytime the water turns cloudy. When looking at the results of that water test, first look at the chlorine level. Water can start to become cloudy with a chlorine residual of 1ppm or less.

If there is a good chlorine residual in the water you should next look at the pH and alkalinity. If they are high (pH above 8, alkalinity above 180) then there is a chance that they are to blame. The higher they are, the more likely they are the cause, especially if there is also a lot of calcium or other dissolved solids in the water.

Another good indicator for what caused the water in your pool to turn cloudy is the timing of the cloudiness. If you first noticed the water go cloudy after a heavy use, very warm weather, or a rainstorm, then the cloudiness is probably due to a lack of chlorine. If the water goes cloudy after raising your pH, alkalinity, or calcium hardness, then the problem is most likely water balance related. If the cloudiness came right after an algae bloom, then it is most likely dead algae.

Treating Cloudy Water

To treat pool water made cloudy by a lack of chlorine, keep adding chlorine to the water until the water maintains a chlorine residual of 2ppm or more. To treat water made cloudy by high pH/alkalinity, simply add a pH/alkalinity decreasing chemical until their level decreases to an acceptable level. In the case of a salt pool, you may need to also increase the salt system’s output. In all cases, keep the pump running 24 hours a day until the water is completely clear.

If your water test results shows no obvious cause for the water turning cloudy, then the issue is most likely with the pool’s filtration system. Either there is an issue with the filtration system itself, or the particles are simply too fine for the filter to catch.

Start treatment by adding a clarifier to the water. Clarifiers work by grouping ultra fine particles together so that the pool’s filter can more easily filter them out. You should again keep the pump running 24 hours a day, until the water clears. If the water hasn’t cleared after two or three treatments then the pool’s filtration system could be to blame for the cloudiness.

When troubleshooting your pool’s filtration system, the first thing to consider is the run time of the pump. If the pump is running for less than 8 hours a day you run the risk of the pool not filtering enough to maintain water clarity. If running your pump for 24 hours straight makes a noticeable difference, continue running the pump until the pool clears, then ensure that the pump operates for at least 10 hours a day for the entire pool season. If your pump is already running for 10 or more hours a day then the next thing to consider is the filter.

If you own a sand filter, and the sand is 7 or more years old, it could be time to change the sand. By changing the sand you will restore the efficiency of the filter and allow it to filter to a finer degree. If you own a cartridge filter you can first try cleaning the filters with a specialized pool cartridge cleaner. If that doesn’t work you will need to replace the cartridges to restore the filter’s efficiency.

As you can see, there are many potential causes for cloudy water. Water balance, filtration issues, and a simple lack of chlorine can all lead to water clarity issues. Knowing how to spot the difference between them, and getting your water tested, is the only way to know how to properly treat the issue, and get your pool clear. 

Did you like this post? Like us on Facebook( or follow us on Twitter (@thespashoppe) to get notified when new blog entries are posted!

The Spa Shoppe

(905) 666-5333

1545 Dundas St E
Whitby, ON L1N 2K6



Monday – Friday: 10:00 AM – 7:00 PM

Saturday: 10:00 AM – 5:00 PM

Sunday: 11:00 AM – 4:00 PM

Apply for Financing Online