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Using Muriatic Acid To Clear A Green Pool Quickly

Has your swimming pool turned green and you are looking for a solution to fix it quickly? In this article, we will discuss why your pool is green and how you can use muriatic acid to adjust the pH level and get your pool looking clear again.

swimming pool with green algae
Swimming pool with green algae.

Why is My Pool Green?

If your swimming pool water has turned green, then there is definitely a reason behind this happening. There are a few reasons and causes for why it may have turned green, so let’s explore them.

Your swimming pool may be green because of:

1. Algae

This is most often the main reason why your pool is green. Algae can bloom if there is a lack of circulation in the pool or if the chemical balance is off – particularly if the chlorine is low or the pH and/or stabilizer levels are incorrect.

It will most commonly occur during hot weather, but no matter when it blooms, it will create green and cloudy water. Avoid using your swimming pool if the water is green because it could make you ill.

2. Oxidized Metals

Oxidized metals such as copper and iron can cause your swimming pool water to turn green.

These metals, which are in the water, can react to the chemicals in the pool.  Too much chlorine added to the water can cause the metals to oxidize and turn green, so be aware of that too.

You can test the metal levels with a metal test kit.

3. The pH and Chlorine Levels are Not Right

You want your swimming pool to have a neutral pH balance, around 7.4-7.6. If it is not, it can affect how well chlorine can do its job. Therefore, even if you do have the correct amount of chlorine in the pool, the pH will ultimately affect its efficiency.

Stabilizer (cyanuric acid or CYA) also interferes with the effectiveness of chlorine. If it’s too high, or too low, the chlorine will not work properly. Keep stabilizer at 30-50 ppm.

And naturally, if the chlorine levels are too low, algae can grow.

4. Phosphate Levels are Too High

Having too much phosphate in your pool can cause the proper pool chemistry to be off and phosphates are actually a food source for algae.

Phosphates can get too high in your pool if there are too many dead leaves and other organic matter getting into your swimming pool. Make sure you skim and vacuum your pool regularly.

5. The Filter is Not Working

Over time, you may need to get your pool filter cleaned, repaired, or replaced. It is a very important part of a healthy and functioning pool as it gets rid of the debris and dirt that gets into the pool.

Be sure to check the filter and the pump to see if it needs replacing and if so, get your pool some brand new parts so you can enjoy a clean pool again.

Related Reading: What to Do if Swimming Pool Filter Not Filtering Algae

Does Muriatic Acid Kill and Clear Algae?

Muriatic acid itself will not kill and clear algae on its own, but it is definitely needed to help get rid of the algae. Using muriatic acid is a part of the process to balance the alkalinity and pH levels in the pool before you can add chlorine.

Related Reading: How to Clean Pool Cartridge Filter (Using Muriatic Acid)

3 Reasons to Add Muriatic Acid

When you have a green pool and want to clear it quickly, muriatic acid is the best substance when pH levels are incorrect because:

Reasons To Add Muriatic Acid To Your Green Pool

Reason 1It lowers the pH level
Reason 2The chlorine will perform better as the pH is not too high
Reason 3It can also clean any pool tiles and stains and dissolve calcium deposits

How Much Muriatic Acid is Needed?

When adding muriatic acid to your pool, generally you want to add 20 ounces of muriatic acid to 10,000 gallons (45,461 L) of pool water. This will result in a decrease in the alkalinity by 10 parts per million.

It is very important that you add muriatic acid to the pool water gradually and step by step, and not all in one go. It’s better to have added too little than too much. You need to keep retesting the water until you have achieved the right pH level.

Related Reading: What To Do If You Add Too Much Muriatic Acid To Pool

How to Treat a Green Pool with Muriatic Acid

Here is a step-by-step guide to show you how to treat a green pool with muriatic acid.

Step 1: Test the Pool Water

The first step is testing the pH and alkalinity of your pool water so you know where it is at. Ideally, you want the pool at a pH level between 7.4 and 7.6.

Man Testing the Swimming Pool Water
Man testing the swimming pool water.

Step 2: Wear Protective Clothing

Be sure to wear safety goggles, gloves, and other protective clothing, as muriatic acid can cause burns if it has exposure to the skin.

Step 3: Add Muriatic Acid to the Pool

You can add the muriatic acid to the pool as long as you have the pump running and you add it at the deep end first then walk around the pool adding it. Ensure you don’t stop and inhale the fumes or cause big splashes.

If desired, you can choose to dilute the muriatic acid with water before adding it to the pool, but it is not necessary. Some people may choose to do this to be extra safe when handling the acid.

Step 4: Check Stabilizer Levels

Having too much stabilizer in your pool will affect the effect of chlorine. You want to ensure you have 30 to 50 parts per million (ppm) of stabilizer. Check that the alkalinity is in the correct range as well at this step. Alkalinity should be 80-120 ppm.

Step 5: Clean the Pool and Filter

Use a net to scoop out all of the leaves and debris. Next, brush the walls and floor of the pool aggressively. The idea is to loosen any algae.

Now clean the pool filter. If you have algae, chances are the filter will be full of it.

Brushing pool floor and walls
Brushing pool floor and walls.

Step 6: Shock the Pool Using Chlorine

After 30 minutes to an hour after adding the muriatic acid to the pool, you can then shock the pool with chlorine (if the pH and stabilizer levels are correct.

Add around 4 gallons (18 L) of 12.5% liquid chlorine to 10,000 gallons (45,461 L) of pool water. It’s best to do this at night to maximize the chlorine effectiveness. You’ll want the chlorine levels to be 30 ppm or more.

You can also use pool shock instead of liquid chlorine to get the job done.

Add it in the same way as you did the muriatic acid by pouring it into the deep end and walking around the pool, or even pouring it by the jets so it can circulate around the pool that way.

You can purchase chlorine on Amazon to aid you in shocking the pool.

In The Swim - Calcium Hypochlorite Chlorine
  • Powerful pool chlorine/shock treatment - great for killing algae & everyday chlorination.
  • It can be used in all pools & doesn't raise stabilizer levels
  • Clears cloudy & dull water

Step 7: Run the Pump for 24-48 Hours

It is important to allow muriatic acid and chlorine to do their job. Leave the pool overnight and test it again the next day and shock the pool with chlorine again if needed.

Always keep the pump running for the whole day for at least a few days. Be patient and don’t rush the process. You will know that it is working when any algae in the pool start to turn gray and die. The pool filters will then take care of cleaning it up.

You’ll likely need to clean the filter out several times if you have lots of algae.

Step 8: Vacuum to Waste

Now it’s time to vacuum the pool. You should be able to see the bottom of the pool again. Set your filter to “waste” and start vacuuming.

A woman vacuuming the swimming pool floor
A woman vacuums the swimming pool floor.

Related Reading: Green Pool – Guide to Easily Preventing & Removing Pool Algae

How Long will Muriatic Acid Take to Lower the pH Level?

It can take a few hours to adjust the pH level in the pool, but for it to really mix in completely with all the water, you would want to give it about 4 – 6 hours before retesting the pH level again.

It is important to always run the pump and allow the muriatic acid to circulate throughout the entire pool. So it may take 4-6 hours for all the water to mix together and then you can retest the pH level.

Related Reading: How to Lower the pH in your Pool

How Long Will it Take to Clear Green Pool?

It can take a few days or a few weeks to clear a green pool depending on how bad it is and how well you add the muriatic acid and the chlorine to the pool.

So if you have plans to enjoy your swimming pool next weekend, ensure you get it cleaned up at the beginning of the week to avoid stress and disappointment!

Adding Chlorine after Muriatic Acid: How Long to Wait?

You want to wait around 30 minutes to 1 hour after adding the muriatic acid before you start adding any chlorine to the pool. You don’t want to add them together or mix them together at the same time because that can cause a dangerous reaction. And don’t add the chlorine until your pH test results are 7.4-76, otherwise, you’re wasting your time and money.

However, as long as the pumps are running while you add the acid and you allow it to be dispersed around the whole pool, then you are able to add the chlorine not long after.

Related Reading: Can You Add Pool Chemicals All At Once? (answered!)

Common Questions

Is Shock the Same Thing as Chlorine?

Shocking is the process of adding a chemical to your pool to kill off bacteria and organics.

It can be done by adding a high amount of chlorine. However, there are other products that people may use to shock their pools that are not chlorine based.

How Long Until You Can Swim in Your Pool After Shocking?

You will want to wait at least 24 hours after shocking the pool before you swim in it. You may want to wait a few extra days if you see that the pool is still clearing up any algae from the pool as well.

The chlorine levels should be back under 5 ppm, the algae should be cleared up and the pH should be 7.4-7.6 before swimming.

Related Reading: How Long After Shocking a Pool Is It Safe to Swim?

What Happens if I Put Too Much Muriatic Acid in the Pool?

If you overdo the muriatic acid, don’t freak out. If the pH has gone way too low, you can always increase the pH using by adding baking soda, borax, or soda ash.

Related Reading: What To Do If You Add Too Much Muriatic Acid To Pool

3 thoughts on “Using Muriatic Acid To Clear A Green Pool Quickly”

  1. Ph is very to 3.6 and chlorine is 3.0, my water pool still green after almost 12 hours of treatment I’d Muriatric acid.

    • Hi Manny,

      Your pH is way too low. Here’s what you need to do to fix your green pool.

      1) Test the Water Again: It’s essential to maintain the right pH and chlorine levels in your pool. Test the water with a reliable test kit to ensure the accuracy of your measurements.

      2) Adjust pH: A pH level of 3.6 is too low. It should typically be between 7.2 and 7.6 for a pool. To raise the pH, add soda ash in small batches. Run the pump then retest the water after a few hours and continue adding more soda ash if the pH is still low. Don’t add the soda ash in one big batch. That could cloud the water.

      3) Brush: Brush the pool walls and floor to help remove algae clinging to surfaces. Vacuum the pool to remove any debris and dead algae. Then clean the filter.

      4) Add Chlorine Shock: A chlorine level of 3.0 is fine, but if your pool is green, it’s likely due to the presence of algae. Shock your pool with a strong chlorine dose to kill the algae. You can double the dose if it’s quite green.

      5) Algaecide: Consider using an algaecide to further combat the green water. Follow the manufacturer’s instructions on how to apply it.

      6) Filtration: Ensure that your pool’s filtration system is running effectively. Backwash and clean your filter as needed to remove debris and dead algae. Keep the filter running continuously for 2-3 days.

      7) Patience: It can take some time (a few hours to several days) for the water to clear up completely, so be patient. Just keep dumping in more chlorine and checking the pH if the water is still green. Continue to monitor and adjust the water chemistry as needed.

  2. I made a mistake adding the chlorine first before adding muriatic acid, still after 24 hour my pool clear up a little but still obviously colored green . What should I do .? I am frustrated m need help


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