Why a cloudy pool after rain

cloudy pool water
cloudy pool water

Have you ever noticed that after it rains you have a cloudy pool? Have you ever stopped to wonder why? If you have then, we are going to tell you why.

Pool Basics 101 Cloudy Pool Water

First and foremost you need to know the basics of your pool chemistry to understand a cloudy pool. Your pool is water filled with chemicals to kill bacteria and other disease-causing micro-organisms. Pool chemistry is very delicate. Rainwater can either be alkaline or acidic when it comes in contact with your pool water.  It can change the pool water’s chemistry drastically.

Part of what makes your pool cloudy after it rains is these chemicals:


Different kinds of Pool Chemicals

  • Chlorine

Chlorine gets added to pools as a residual sanitizer. What this means is that chlorine will kill any bacteria in the water that might harm you. However, chlorine needs to be added in measured amounts because too much or too little chlorine is not good. When it rains, the amount of chlorine in the water temporarily remains the same, but the amount of water and contaminates in the pool changes. These small changes combined with the effects of other chemicals in the pool can bring about the cloudy effect you see after it rains, especially when your chlorine starts to drop.  Test chlorine regularly and calculate how much to add to the pool water at www.poolchemicalcalculator.com .

  • Phosphates

Phosphates are not added directly to your pool. They are introduced inadvertently by organics such as grass, fertilizer, lotion and well water. Phosphates found in nearby grass in the form of fertilizers. Hence, when it rains, phosphates can be transported and dumped into the pool giving algae and other bacteria the opportunity to grow and multiply.

Other reasons that can make your pool cloudy after it rains:

  • Bacteria

When micro-organisms clump together, they can form impenetrable walls that make your pool cloudy looking. If there is nothing blocking light from entering your pool, the light is reflected back, and your pool looks clear. When bacteria and contaminants have increased to a significant proportion such that it clumps together blocking light, that’s when you start seeing a cloudy formation in your pool.

  • Algae

Algae consists of tiny microscopic organisms that grow and multiply when there is an abundance of sun, water, air, nitrates and phosphates. Fortunately for the Algaecide in your swimming pool, sun, water, and air are readily available agents. Nitrates and phosphates get added when it rains.  Nitrogen is bonded to other compounds to make it nitrates.

cloudy pool after rain
cloudy pool after rain

As the rain water reaches your pool, the nitrates and phosphates dissolve into the pool, providing the fourth and fifth element algae needs to grow and multiply. Once there are a lot of algae, you’ll start to get that cloudy pool look. 

  • Debris

On windy days, leaves, twigs, and other debris blow into the water. Fortunately, fishing out this debris from your pool is easy. You will need a vacuum and a skimmer to make your life easier. Skim the dirt out and then vacuum the pool before checking to see if the pool chemistry in the water has changed.

So what do you do after a rain storm?


The very first thing to do is clean all the large debris out of the pool and scrub the walls with a pool brush.  A suction side cleaner or robotic pool cleaner can help with cleaning up of the medium to smaller debris.  Now that all the debris is gone either take a sample of water to the pool store or use a test strip to measure the chemistry levels.  The chemistry report can quickly identify the source of the cloudy pool water.  Calculating how much of each chemical to add can be hard.  I use pool volume and chemical calculator at www.poolchemicalcalculator.com because its quick and easy to use on my phone and has an offline mode.  

Now you know what makes your pool cloudy after it rains, and how to make it clear again.