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Clearing Out Green Pool Water – A Quick Guide

green pool water

Green pool water. Image by Gerd Altmann from Pixabay

If you’ve let pool water sit for a while, you may notice it changing green. To clear out green pool water, follow the steps outlined below.

What Causes Green Pool Water?

Green pool water results from algae buildup, and algae grow in pools where there’s a chemical imbalance. In order to correct the problem, you’ll need to rebalance the chemical content of your pool—typically by making sure chlorine levels are sufficiently high.

First, Run Some Tests

To start off, you’ll want to test the chemical levels and pH of your pool. Chemical tests will allow you to do this. Imbalances may take the following forms.

Low chlorine content

If the chlorine content in your pool is less than 1 ppm (part per million), you’ll get algae growth. If that’s the case, the course of action you’ll need to take is to shock your pool.

High pH

In some cases, you might have enough chlorine, but other chemical issues may be causing algae growth as well. If the pH level of your pool is too high, it may be rendering your chlorine ineffective.

frog and butterfly in pond

Image by Frank Winkler from Pixabay

Lots of phosphorous

Another issue might be an excess of phosphorous in your pool water. High phosphate levels may result from organic debris in the pool or spray fertilizers. Algae thrives on phosphates, so cutting down those levels should help.

High levels of cyanuric acid

Chlorine tablets often include stabilizers such as cyanuric acid, and a buildup of those stabilizers in your pool can essentially “lock” the chlorine in place, preventing it from doing its job. If this is the case, the only solution is to drain a couple feet of water from your pool and refill it to dilute it.

None of the above

If your pool’s chemical levels are all fine, you might have an issue with your filter. If your pool’s filtration system isn’t working properly, you’ll need to get it repaired to make sure it circulates everything properly. High humidity and other factors may also contribute to it. For instance, if you’re in a humid area like North Carolina or Florida, you’ll have a higher chance of seeing algae in your pool.

Run the Filter

Once you’ve determined the cause of your green pool water, you’ll need to get the filter running. If you have any debris in your pool, clear it out, and change out any parts that you need to.

If you have a diatomaceous earth (DE) filter or sand filter, you’ll need to backwash it first for a bit before treating your water. Cartridge filters need to be cleaned regularly, particularly as you run your treatments.

Balance the pH

When you’re certain your filter is working properly, you’ll start treatments by balancing out the pH of your pool. For shock treatments, you’ll want to get the pH to about 7.2 or lower for it to work properly.

To raise the pH, add sodium carbonate. To lower it, add sodium bisulfate. You’ll probably need quite a bit for larger imbalances, so make sure you get enough.

After adding the chemical, run your filter to circulate it throughout your pool.

Scrub the Pool

Next, it will be time to scrub the edges and floor of your pool. Algae often clings to the sides of pools, so this is a necessary step to getting it cleaned out.

Shock and Treat

When you’ve got everything scrubbed and ready to go, it’s time to shock your pool. This is done by adding tons of chlorine. A few pounds of granular pool shock with about 70% available chlorine should do the job.

With the filter running, spread the pool shock all over your pool and let it go for a few hours. After that, add some algaecide. If you have high phosphate levels, using a phosphate remover will help with that.

After adding your chemicals, let the filter run for 24 hours. After that point, you shouldn’t have any more green pool water. However, you’ll still have some cloudiness and debris, meaning more filtering and scrubbing will be necessary.

Final Cleanup

After your initial filtration, you should see a lot of dead, colorless algae on the bottom of your pool. Using a brush or vacuum, clear up as much of that algae as possible.

It will typically be necessary to keep running your filter after the initial shock to get rid of the cloudiness. If you have a sand filter, that could take a couple weeks. If you have a cartridge filter, it’ll only take a couple days, but you’ll also need to clean it daily until the pool clears up.

Once this process is over, you should have crystal clear pool water again!

Prevent Green Pool Water in the Future

After removing all algae in your pool, you’ll want to take steps to prevent green pool water in the future. Some of these steps will help:

  • Keep pool chlorine and pH levels constant with regular chemical treatments.
  • Cover the pool when not in use to keep debris out of the water.
  • Run the filter regularly to keep the water clean.
  • Keep your filter in good repair.

Certain components can also be covered by a home warranty, further helping you keep your pool ready for those hot summer days.

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