Pool Equipment Troubleshooting

Muriatic Acid to Lower Your Pool Alkalinity

 How to apply muriatic acid to decrease your swimming pools alkalinity.

By Allen Hayward

You can balance the alkalinity level of your swimming pool without spending a lot of money on chemical additives. All you need is some good quality muriatic acid. But you don’t simply pour the acid into the water and call it a day. That’ll cause problems for you.

A high alkalinity level in the water could end up damaging your pool and its circulation system. Once the pH level rises, the water chemistry becomes all messed up. You can affordably reduce the alkalinity of your pool by using muriatic acid. This requires patience, a bucket, and the ability to follow simple safety instructions.

What is Muriatic Acid?

Muriatic acid is traditionally used in the field of masonry. Since masonry surfaces are naturally alkaline, muriatic acid can reduce the pH level on these surfaces and keep them cleaner. That way, paint can stick to it better.

The human stomach naturally produces muriatic acid to increase the pH level in the gut. This will eliminate microorganisms that cause you to get sick and assist with the digestion process.

In a swimming pool, the muriatic acid can reduce the pH and alkalinity levels in order to balance the chemistry of the water. The muriatic acid formulated for swimming pools generally has a lower hydrogen chloride concentration than what you’d find in masonry-supported muriatic acid products.

All chemicals have a functioning agent, just like all medicine has an active ingredient. You just need to make sure the proper concentration of the agent is in your chemicals because that is how you’ll balance the chemistry of your water in an easier, safer way.

Pools with cartridge filters probably came with muriatic acid already. It is used to provide a deep cleaning to the filters by eliminating the slimy residue that tends to accumulate on them. If you have muriatic acid for filter cleaning purposes, then you can also use it for reducing the alkalinity in your pool water too.


Understanding pool chemistry tends to be rather difficult for many people. Experienced pool owners can even make mistakes when treating their pool water.

One thing you should remember is that alkalinity levels will eventually decrease by themselves. However, you can’t leave high levels of alkalinity in your water for very long because algae will start to grow quickly. That is why you must reduce your alkalinity levels with the appropriate chemicals.

High pH levels mean low acidity, causing the water to become softer and accumulate calcium. The water will appear flaky and scaly too. As a result of these conditions, the filter and circulation system of your pool will get clogged. Then you’ll have more to clean out of the water with your sanitizing chemicals. This will prompt you to add more chlorine to combat the problem. Then the pH levels and alkalinity will rise.

When the pH is high, the calcium in the water turns harder. The natural unstableness of pH requires more alkalinity to slow it down. When you use chemicals to reduce pH, you’ll also reduce the alkalinity too. But the pH will lower more when you lower the alkalinity. So, it is best to reduce the pH to about under 7 ppm (parts per million). Make sure you alter the pH levels in smaller stages by conducting daily testing and adding more chemicals if needed. You should get the alkalinity levels back on the proper path if you do this.

Having balanced alkalinity ensures your pH levels are good for your pool. It also assists the sanitizer in stopping contaminants from spreading throughout your pool.

High Alkalinity with Low pH

Even though alkalinity and pH get reduced together, the pH lowers much faster than alkalinity. This could result in high alkalinity and low pH in your pool water. Excessive amounts of cyanuric acid getting added to the water will cause this to happen.

Outdoor pools require chlorine stabilizers, but they must be used properly or else the water chemistry will suffer an imbalance. Every chemical you put in your pool will have an effect on the pH and alkalinity levels but at different rates. Any attempt to adjust these levels will still cause one to be higher than the other.

Reducing Alkalinity in the Pool

Virtually every pool supply shop sells a “pH Decreaser” product. The main functioning ingredient of the product is sodium bisulphate. It is formulated to reduce pH and alkalinity levels. Although muriatic acid is a good alternative to this because it is already available with your filters. But even if you have to purchase muriatic acid, it is much more inexpensive than purchasing a pH Decreaser. You just need to apply the muriatic acid properly to the water in order to reduce the alkalinity.

Safety is Most Important

Muriatic acid must be handled carefully because if it gets on your skin, it’ll burn it within seconds. And if you inhale the vapor of the muriatic acid, it could negatively affect your respiratory health. Purchase the proper accessories to stay protected as you use the acid.

Water Testing

Don’t add any chemicals until you have tested the alkalinity and pH levels of your pool. Test strips are commonly used for this, but you can get a more accurate reading from digital test kits.

No matter what the reading shows, muriatic acid must be applied in stages when reducing the alkalinity in the pool water. That will take a lot of time, though.

Determine the Acid Quantity Needed

Find out the water gallon capacity and the alkalinity level and pH level of your swimming pool. When reducing these levels, calculate the amount of muriatic acid needed to lower your pH level just under the ideal amount. If you do this, your alkalinity level should be normal. After that, use the pump to aerate the water and slowly increase the pH level.

The muriatic acid product label should indicate the amount of acid to add to the pool. If for some reason the label doesn’t tell you this, then use an online calculator to do the calculations yourself.

Deactivating the Pump

If you’re trying to stabilize your pH level while greatly reducing your alkalinity, then deactivate the pump prior to applying muriatic acid to the water. After the pump is activated, the chemicals in the water will circulate and mix together. In addition, oxygen gets added by the bubbles shot into the water.

As more oxygen enters the water, the muriatic acid becomes more effective on the pH. To greatly reduce the alkalinity, deactivate the pump to slow down the movement of water.

Muriatic Acid Addition

When you want to add muriatic acid to the pool water, it is better if you don’t just pour the acid directly into the water from the canister. Instead, dilute the muriatic acid in tap water so that it is less hazardous and simpler to handle. It only takes a bucket and a couple of extra minutes.

The best water-to-muriatic acid ratio is 10-to-1. After you add the proper quantity of muriatic acid to the water, use a stir stick to mix it all around. The stick can be made of wood or plastic.

Make sure water is added to the bucket before you do this. Adding the muriatic acid first will cause a dangerous chemical reaction. So, it goes water first and then muriatic acid second.

Go to the deepest end of the swimming pool and pour the mixture from the bucket into it. If your pool already has a high pH level, then gradually walk around the perimeter of the pool and gently pour the mixture into it. The water will be exposed to more air while the chemicals are able to circulate.

Make sure the bucket is rinsed thoroughly of all muriatic acid remnants once you’re done. No other chemicals should be used in the bucket or else an explosion might occur.

Let the Acid Do Its Business

There are two ways in which you can approach this. First, you can take the safest approach of turning on your pool pump and allowing the muriatic acid to circulate in the pool water for a minimum of 30 minutes. That will stop the muriatic acid from falling to the bottom surface and damaging it.

Alternatively, you can just let the muriatic acid work its magic on the alkalinity without turning on the pump. Professionals call this approach “pooling.” This is not always the best approach, though, because the muriatic acid is strong enough to damage the pool floor if it settles there. To prevent this from happening, the pool floor must regularly be brushed.

Of course, these approaches to reducing alkalinity while not affecting pH are merely opinions. One thing that is true is muriatic acid can damage pool surfaces. To make sure this doesn’t happen, activate the pump for 30 minutes as soon as you add the muriatic acid to the water.


To increase the pH a little bit, keep the pump running to add air to the water. This will help reduce the chances of increasing the alkalinity as you use chemicals to increase the pH level.

The best approach to aeration is positioning the return jets toward the top and turning the pump on full blast. All other water features must be turned on too. Alternatively, a fountain or aerator device can do the same thing.

Test the Water Again

After muriatic acid is added to your pool water, conduct another test of the water chemistry. If the alkalinity is still too high, add a little more muriatic acid. If the pH level is reduced while the alkalinity level is just fine, then aeration can continue.

The next day, test the pH level again to see if it is higher. If it is not, then use a little pH increaser chemical on the water.

Repeat the Process

You will basically repeat this process numerous times to reduce the alkalinity level to where it needs to be. Just keep testing the water, adding muriatic acid gradually in small amounts, and repeating again. If you have trouble achieving the right levels of alkalinity and pH, take a sample of your pool water and bring it to your local pool store and have them test it out. Perhaps the accuracy of your tests is off.

Balance is the Key

Balancing the water chemistry of your pool on a regular basis can prevent algae, corrosion, staining, stomach bugs, and other water-based illnesses. Keep checking the water and using more sanitizer, especially if lots of people have been using the water.

If you can keep your water chemistry managed properly, you won’t need to alter the alkalinity levels so much. But if you’ve let the chemistry become imbalanced, just add some muriatic acid to help get it back to the right level.


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