What Causes Cloudy Pool Water?

Cloudy Swimming Pool with green algea

Nothing is more unappealing than milky or murky water that’s slimy to the touch or resembles swamp water. You need to learn how to clear cloudy pool water–and fast! 

While the causes for cloudy pool water can overlap with the causes for cloudy aquariums, how you get rid of cloudy water in a fish tank is different from removing murky water from your pool. Whether you’re a new pool owner or wondering why your saltwater pool is cloudy, Pool Care Guy has the insights you need to turn that swampy water into crystalline perfection.

What’s Wrong With Murky Water?

Cloudy pool water is more than just aesthetically unappealing, it can be dangerous. For example, cloudy pool water can indicate a build up of debris and particles, which can damage or inhibit your pool’s filtration system. This can make it harder for chlorine and other sanitizers to reach all areas of your pool or render your filtration ineffective. 

Ineffective filtration can result in overgrowth of bacteria and algae, which can produce recreational water illness (RWI). This can cause your water to become contaminated with germs like:

  • E. coli

  • Giardia

  • Cryptosporidium

In addition to causing illness, it can make it more difficult for swimmers to see. If your pool sees a larger volume of swimmers, this can pose a safety risk. Divers may dive into shallow water or swimmers might swim into each other, and these can result in injuries to swimmers.

Three Main Causes for Cloudy Water

It doesn’t matter what type of pool you have or the season you swim in, pools get murky. Let’s dive into the three most common reasons your pool water is cloudy and how to treat it.

Algae Growth

A common misconception about algae is that you only have an algae problem when your water turns green. There are different types of algae and they come in different colors (green, black, pink, and yellow/mustard). Different colors of algae represent the different types, and each type requires a unique intervention to get rid of it.

If your chlorine levels are normal (as this is a common cause for green water), identify the color of the algae. Once you determine the color, you need to find the corresponding algaecide to add alongside a clarifier (clarifiers are optional):

  • Green algae: Shocking your pool and using chlorine is the best way to get rid of green algae. You can also use a brush and vacuum to scrub away or suck up any remnants of the algae.

  • Yellow/mustard algae: This algae is resistant to chlorine and is derived from green algae. It sticks to surfaces and can look like dirt or sand. Look for products that focus on both treatment and prevention, such as a three-month or two-month algaecide.

  • Pink algae: Pink algae is also a resilient bacteria and can survive even in pools with high levels of chlorine. Balance your chemicals, shock your pool, brush the pool thoroughly, vacuum it, and add a biguanide algaecide and oxidizer.

  • Black algae: This is the most difficult type of algae to get rid of. It has deep roots and multiple layers. Ensure your chemicals are balanced, sanitize all pool items, scrub the algae, and add an algaecide with an active ingredient that has a concentration level of at least 30%. Then, triple-shock your pool and scrub again.

If you do not get rid of all the algae, no matter the type, it will grow back pretty quickly. If your water has not cleared up after seven days, consult with your local pool store for more information.

Low Pool Runtime

If your pool is not running for at least eight hours a day, it can cause your water to become cloudy. Even if you don’t use your pool regularly, when it’s running 24/7, the circulation ensures your chemicals and pool water are mixing properly.

When you run your pool, your skimmer sucks up debris that can fall or collect in your pool. Debris that just sits in your pool can overwork your chlorine, because it will spend all of its time trying to eat at the debris. With a skimmer or filter basket, you can easily move debris out of the way so the chlorine can focus on the chemical balance of the pool.

If you’ve had a low runtime for your pool, an easy fix is to backwash your pool at least once a week or run your pool more often. 

There’s a Chemical Imbalance

Another common reason your pool is cloudy is that there’s a low chlorine level or other chemical imbalance. When there isn’t enough chlorine present, bacteria can grow in your pool and make it cloudy or even result in algae growth! This can also happen when there’s an alkaline or pH imbalance.

You can avoid this by regularly testing your pool water at least once a week. When chlorine is low, add another tablet or shock your pool and let it run for a few days. If your pH is too low or too high, you can adjust the levels accordingly.

The Bottom Line

There are numerous possible causes for your cloudy pool water. Check for chemical imbalances, run your pool regularly, and tackle algae head-on as early and as thoroughly as possible!

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