What is Alkalinity

Alkalinity measures calcium, magnesium, and other acid-moderating compounds that act as a buffer to pH change. What is essential to understand about alkalinity is that it helps stabilize the pH balance, preventing sudden pH changes in your water and thus keeping the pH within a normal range. There is often some confusion about pH and alkalinity regarding water chemistry. The misconception is that these are the same thing.

When you measure pH, you check how acidic or alkaline the water is. The range goes from 1 (very acidic) to 14 (very alkaline), with 7.4-7.6 being neutral and a place where Chlorine works at its best. 

On the other hand, alkalinity (or total alkalinity) is not measured like pH on a scale but in parts per million (ppm) of those compounds mentioned prior. The recommended range for a pool or hot tub water alkalinity should be between 80 and 120 parts per million. Any good water testing kit can help you determine the range, or you can take a sample of water to your local pool or hot tub store.

Why Alkalinity is So Important
If your Alkalinity is Below 80 parts per million (ppm), alkalinity will result in your water being too Acidic. This can cause:
  • Corrosion of surfaces and equipment
  • Etching and staining of surfaces and equipment
  • Burning or itching of the eyes and skin
  • Water may turn a shade of green
  • Wild fluctuations in pH levels


If your alkalinity exceeds 120 parts per million (ppm), alkalinity will make your water too alkaline. This can cause:

  • Scaling of surfaces and equipment
  • Burning or itching of the eyes and skin
  • Water may turn cloudy
  • A high pH level is more challenging to lower

There are many reasons why alkalinity will go up or down in your pool or hot tub water. It can be from natural environmental or bodily causes and everyday treatment chemicals. Keeping Alkalinity in the range makes your swimming or soaking experience more enjoyable and is very important to the life of the pool or hot tub and its components. 

Adjusting the Alkalinity is something that should be done incrementally. In other words, it is better to make slight adjustments when the Alkalinity gets high or low than to wait for the Alkalinity to get way off and try to adjust it all at once, which can make the processes more difficult. If the Alkalinity is way off, I recommend adjusting and then retesting after 24 hours and adjusting again if necessary.

What Causes Alkalinity to Rise

If your pH level goes up, it will begin to increase your alkalinity. An increase in pH typically comes from body lotions or sweat washing off into the pool or hot tub. You could also be using a high-alkalinity water source. It’s also not uncommon for owners to go a bit overboard when shocking their water, and since the chlorine-based shock ingredients cause alkalinity to rise, that will naturally raise your alkalinity.

To lower the Alkalinity level, you can use Muriatic Acid (liquid) or Sodium Bisulfate (granular). Both can also be used to adjust pH. It is just applied differently. I would only recommend Muriatic Acid for Swimming pools, as Muriatic acid is highly caustic. It can burn your skin, and the vapor from muriatic acid can cause respiratory problems. Read the directions or consult the store you purchased it from for proper use and precautions. Most pool stores recommend this for high alkalinity because of its low cost compared to Sodium Bisulfate, and a lot of liquid acids can go a long way in a large pool. 

That being said, both can significantly lower your alkalinity while keeping your pH as stable as possible. The directions for both types of acid are the same. Start by shutting off your pump before adding the acid. When the pump runs, it circulates the acid, but it also adds oxygen by churning, causing the water to bubble. The oxygen then amplifies the effects of the acid on the pH, which is fine if you are trying to lower both pH and alkalinity.

What causes Alkalinity to Fall

If your pH level is on its way down, it will eventually begin to decrease your alkalinity. A decrease in pH can be caused by sweat or excessive rainwater entering a pool and diluting it. Acid rain can directly drive both your pH and alkalinity levels down. Shock can raise pH, as explained above, but a typical chlorine tablet has the opposite effect. Dissolving into your pool water will lower your pH level and alkalinity. 

To raise the Alkalinity level, you would add Baking Soda (Sodium Bicarbonate). Baking Soda can raise the pH of the water slightly because, again, both Alkalinity and pH are tied together. This also makes it perfect for hot tubs, as they typically need only minor Alkalinity adjustments. So, in turn, it will also fix low pH simultaneously. 

If both the pH and Alkalinity are low, use Soda Ash until the pH reaches the proper level, then use Baking Soda to make further adjustments to the Alkalinity if needed. NOTE: Soda Ash (Sodium Carbonate) and Baking Soda (Sodium Bicarbonate) are NOT the same. Soda Ash is used for adjusting pH and Alkalinity. Baking Soda is primarily for adjusting Alkalinity.

I hope this has been helpful as I am knowledgeable on this subject but would not call myself an expert. In writing this article, I wanted to be as accurate as possible without making it complicated, so I got some help from some online resources to help explain some of the more complicated aspects.

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