How To Lower Alkalinity In Your Pool (2 Proven Methods)



Total alkalinity is a pH buffer that keeps your pool water’s pH level in check by absorbing acids in the water.

The ideal range for alkalinity in a swimming pool is between 80 and 120 parts per million. Letting your alkalinity drift too far outside of that range will eventually lead to issues with your water chemistry.

Let’s talk about why this happens, why it matters, and how to lower alkalinity in your pool the correct way.

Quick answer: Most pool owners use muriatic acid to lower total alkalinity in the water, though you can use dry acid as an alternative. Both of these substances will also lower pH so aerating the water may be required.

Why You Have High Alkalinity

The most likely cause is adding too much pH or alkalinity increaser such as baking soda (sodium bicarbonate) or soda ash (sodium carbonate).

While these products are very effective at raising the pH level of your water, they also contain alkaline substances that will raise your total alkalinity. In the case of baking soda, this increase is substantial.

Aside from that, the cyanuric acid in stabilized forms of chlorine (including most tablets or granular chlorine) also contributes alkaline substances to the water, and these will inflate your total alkalinity reading.

Frequent use of shock treatment such as cal-hypo, trichlor, or dichlor shock can also play a role in raising alkalinity. However, this effect is often short-lived as the shock treatment soon wears off.

Finally, don’t overlook your water source. If you filled your swimming pool with high-alkalinity water, it won’t take much else to push your total alkalinity reading over the edge.

Why High Alkalinity is Bad News

By itself, total alkalinity isn’t that bad for your pool. However, consistently high levels will eventually create a domino effect of issues.

This is because the higher your total alkalinity, the harder it is to adjust your pH level (remember, it’s a pH buffer). Since pH in a pool tends to drift up over time, it may be very difficult to correct if your total alkalinity is left unchecked.

With an elevated pH, the domino effect comes into play:

  • It reduces chlorine’s effectiveness. Free chlorine works best at lower pH, so the higher your pH, the less sanitizing power chlorine has over contaminants. This can result in dirty or under-sanitized water.
  • It turns the water cloudy. Cloudy pool water is a result of calcium and other minerals falling out of solution (they “un-dissolve” if you like), and that tends to happen when the pH of the water gets too high.
  • It leads to calcium scaling. Calcium can be a problem when it falls out of solution because it settles on your pool surfaces and equipment. This is known as ‘calcium scaling’ and it takes some work to remove.

How to Lower Alkalinity in A Pool (2 Methods)

Lowering your total alkalinity is simply a process of “using up” the buffer it provides in the form of acid absorption. In other words, you just need to give it some acid to chew on.

Let’s cover two of the most common acids for lowering alkalinity in a pool, the pros and cons of each, and how to use them step-by-step.

Method 1. Use Muriatic Acid (Recommended)

Muriatic acid comes in liquid form and it’s the most commonly used substance for lowering total alkalinity in a pool.

This acid is fast-acting and very effective at lowering alkalinity (as well as pH), and it’s easy to find in your local area. What’s more, it’s also very affordable as far as pool chemicals go.

However, it is a very strong acid that can be dangerous if not handled or stored properly, so extra care is required. This isn’t unlike many other chemicals you use for regular maintenance, but it’s worth highlighting.

Here’s how to use muriatic acid in a pool:

  1. Test your total alkalinity using a test strip or liquid test kit, then plug your result into our muriatic acid calculator (see below this list).
  2. Put on your protective gear. Wear a long-sleeve top, rubber gloves, goggles or other eyewear, and a face mask to prevent inhaling fumes.
  3. Fill a bucket with water from your pool. The amount of water should be 10x the muriatic acid you will use, as provided by the calculator.
  4. Dilute the acid. Add the muriatic acid to your bucket of water (not the other way around), then use a wooden stir stick to mix the solution.
  5. Slowly pour the diluted muriatic acid into your water while walking around the perimeter of the pool. Avoid pouring near metal fittings.
  6. Keep the pump running for at least an hour to allow the muriatic acid to fully circulate into your water, and twice that for large pools.
  7. Wait a full day before testing your total alkalinity. If the reading is still too high, use the calculator again and repeat the steps.

Here’s the calculator:

Method 2. Use Dry Acid

Dry acid (sodium bisulfate) is a granular acid and a popular alternative for those who aren’t comfortable handling muriatic acid.

This acid is just as effective as muriatic acid in lowering pH and alkalinity, but it’s considered to be safer because it’s not as toxic or corrosive. It’s also easier to store and has a longer shelf-life.

However, aside from being more expensive, it works slower and can cause temporary cloudiness in the water. More importantly, it adds sulfates to the water which can corrode your pool surfaces in high concentrations.

Here’s how to use dry acid in a pool:

Note: This process is very similar to adding muriatic acid; the only differences are less emphasis on safety gear and no water-to-acid ratio.

  1. Test your alkalinity using a test strip or drop test kit, then enter your reading into our dry acid calculator (see below this list).
  2. Wear protective gear. While safer to handle compared to muriatic acid, it’s still acid. Use rubber gloves and protective goggles at a minimum.
  3. Fill a bucket with water from your pool. The ratio of water to acid isn’t as important when using dry acid, so just fill it about halfway.
  4. Dilute the acid. Add the dry acid to your bucket of water and use your stir stick to mix the solution until it’s fully dissolved.
  5. Pour your bucket of diluted dry acid into your pool while walking around the perimeter. Don’t pour too close to the wall or near metal fittings.
  6. Keep the pump running for an hour (longer for larger pools) to allow the acid to fully circulate throughout your pool.
  7. Wait until the next day to retest your total alkalinity. If it’s still above the ideal range, run through these steps once more.

Here’s the calculator:

How to Restore Your pH Level Without Raising Alkalinity

Both muriatic and dry acid will lower your pH level along with your total alkalinity, and this may create a new problem.

If your pH has fallen below 7.2 after adding acid, you’ll need to raise it back up without also raising your alkalinity again. That means avoiding pH-increasing products that contain baking soda or soda ash.

The truth is, aside from draining and refilling, the only reliable way to independently raise the pH level in a pool is by aerating the water.

Aeration infuses the water with oxygen, removing carbonic acid and raising pH in the process. This happens whenever the water is disrupted, such as when it rains, but there are ways to accelerate the process.

Water features are particularly good at aerating the water, including scuppers, bubblers, and waterfalls. Even just pointing your return jets upwards can bubble the surface enough to aerate the water.

Failing that, simply using the pool more and making a splash will be enough to get the pH moving in the right direction.

The Bottom Line

High total alkalinity in a pool in a pool is usually caused by excessive use of pH or alkalinity increasers, cyanuric acid content from stabilized chlorine, or regular shock treatments.

This can make it difficult to keep your pH level within the ideal range, which eventually leads to issues such as high chlorine demand, cloudy or murky water, and potentially even calcium scaling.

Fortunately, applying the right dose of muriatic acid or dry acid will quickly get you out of trouble, but it’s worth weighing the pros and cons of each of these substances in order to determine which one makes sense for you.

Categories: Pool Care, Pool Chemistry