How To Lower Alkalinity Without Lowering pH?


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It is not possible to lower alkalinity without lowering pH. However, to overcome this, alkalinity and pH are both lowered and then the water is aerated to increase the pH level back to the ideal range.

Total alkalinity and pH are vital water quality measurements when it comes to water quality in swimming pools, hot tubs, aquariums, and even soils. 

If the total alkalinity is too high, but the pH level is within range, you may be wondering how to lower the alkalinity level without lowering pH, or if this is even possible.

What Is Alkalinity?

Alkalinity is the ability of water to resist acidic changes in pH and neutralize acidic water. This is why alkalinity is often referred to, as the ‘buffering capacity’ of a solution. 

We use alkalinity to measure how much acid is required to buffer the solution to become neutral or acidic, depending on the pH level required. 

Despite their close relationship, alkalinity and pH are not the same water parameter.

What Is pH?

The term pH stands for the “power of hydrogen”. Measuring pH tells you how acidic or alkaline a solution or substance is, measured on a scale from 0 to 14. Pure/neutral water is in the middle with a pH value of 7.0. As the pH drops below 7.0, the solution becomes more acidic, and if the pH is greater than 7.0 the solution becomes more alkaline (or basic). 

The more hydrogen ions in a solution, the lower the pH, and therefore the solution is acidic, and vice versa. 

Below are the pH ranges in applications that require constant water quality measurements:

  • Swimming Pools: 7.2 to 7.4
  • Hot Tubs: 7.2 to 7.8
  • Aquariums: 6.8 to 7.8, but most aquarists aim for a neutral pH of 7.0
  • Soils: 3.5 to 10.0 – the large range covers a diverse range of crops and produce, however, most soils range from 5.0 to 7.0

Can You Lower Alkalinity Without Affecting pH?

The role of alkalinity is to buffer the pH in a solution and prevent it from decreasing. So, to lower the pH in a solution, alkalinity must also be lowered. This is why when alkalinity is lowered, the pH level will also drop. 

For example, in swimming pools and hot tubs, acids such as muriatic acid or sodium bisulfate are added to decrease the alkalinity, but in turn, it also reduces the pH level. 

Alkalinity is dependent on the presence of chemicals dissolved in water, including bicarbonates, carbonates, and hydroxides. When adding an acid to water, bicarbonates are converted into carbonic acid. It is this chemical reaction that lowers the pH level. The greater the total alkalinity level, the more acid is added. 

So, in summary, any acid added to a fixed volume of water will lower both the alkalinity and pH level. Unfortunately, that’s science. 

Lowering Alkalinity In Swimming Pools & Hot Tubs

In most pools, the total alkalinity in pool water should be anywhere between 100 and 150 parts per million (ppm). This alkalinity range keeps the pH stable and everything else in balance. However, the total alkalinity is not that important if the pH level inside the pool or hot tub is not fluctuating. 

But, if the alkalinity is too high, the pH level will no longer be stable, and it will start to increase along with the alkalinity. So, if the alkalinity and pH levels are both rising, only then should you take action to lower the levels. 

Why Can’t Alkalinity Be Lowered Without Affecting The pH Level In Pools?

Lowering the alkalinity in a pool without lowering pH is very challenging. 

The main issue with adjusting alkalinity or pH is because the two parameters are very closely related. This is why lowering one will eventually cause the other parameter to drop too. Because of that, attempting to lower alkalinity without lowering pH, or vice versa, is not very realistic. 

The only way to lower alkalinity is to lower both, and then raise the pH level by aerating the water. Aeration creates turbulence, which causes carbon dioxide (CO2) to outgas and increase the pH. Aeration is the only way to increase pH without increasing total alkalinity.

So, the key is to increase the surface area of the pool as much as possible. The easiest way to do this is to turn the pool return system on full, towards the surface of the water, and also to blast the pool pump at full capacity. This forces disruption on the water’s surface.

If the pH needs to be increased dramatically, create more disturbance by adding an air compressor with a long hose in the deepest part of the swimming pool. Some pool and hot tub owners also add a spa blower to the return line to increase aeration. The main point is, whichever method you use to aerate the swimming pool will increase the pH without lowering alkalinity. 

But remember, if the pH level is stable, there is no need to adjust the total alkalinity level. 

Lowering Alkalinity In Aquariums

Aquariums that have high alkalinity levels pose a threat to fish. Alkaline waters can cause ammonia spikes, which are toxic to aquarium life and are linked to breathing issues with fish.

The best way to lower alkalinity in aquariums is to dilute the water with purified water that has a low-mineral content. The easiest way to produce purified water is to use reverse osmosis. Another method is to add CO2. Note that both processes will also lower the pH level

A preferred method is to add peat moss, driftwood, or Indian almond leaves. These natural components absorb alkaline elements in the aquarium water, lowering the alkalinity, and pH

If rising alkalinity levels are a common issue, remove calcium-rich stones and rocks that contain limestone or crushed shells that have a high calcium compound. You can also add algae reactors to absorb CO2 or a CO2 scrubber to help maintain alkalinity levels. 

Lowering Alkalinity In Soil

Poor alkalinity levels and low pH impair plant growth by preventing water from reaching the roots, stunting growth, and reducing root development. When soil is too alkaline, it is difficult to lower it because of the close relationship it has with pH.

Alkaline soils have a pH value of 8.5 to 10.0. Alkaline soils are usually from over-liming acidic soils and alkaline irrigation waters. 

To lower alkalinity in soil, the pH must also be lowered. This is effectively done in two ways: chemical methods and cultural methods. 

Chemical Methods

If soils don’t have a reserve of calcium carbonate, applying gypsum is essential to lower alkalinity in the soil. Gypsum is a soft mineral composed of calcium sulfate dihydrate, and therefore the calcium can replace the exchangeable sodium in the soil to lower the alkalinity level.

If the soil contains free calcium carbonates, sulfur is added to lower the soil’s alkalinity. When sulfur is added to soil, it quickly becomes oxidized to sulfuric acid, causing the pH level to drop.

A popular approach is to add organic matter. Not only does adding organic matter to soils successfully lower the alkalinity over time, but it also increases microbial life and improves the soil structure. 

Another more natural way is the addition of molasses. Molasses provide energy for soil fermentation to occur and produce organic acid to reduce alkalinity.

Cultural Methods

If you don’t want to use harsh chemical methods, there are alternative ways to lower alkalinity in soils. 

The first method is to provide proper drainage. Artificial drains can be used to lower the alkalinity in the soil if proper drainage is not available.

Another method would be the use of proper irrigation water. When the water content is reduced in the soil, the alkalinity in the soil increases. Therefore, the soil must be kept moist at all times. 


Total alkalinity and pH are so closely related that lowering alkalinity without lowering pH is very challenging, if not, unavoidable. Adding an acid to a solution will lower the total alkalinity, but it will also lower the pH level. 

If the total alkalinity needs lowering without affecting the pH level, an acid is added, and straight after the water is aerated to raise the pH level without affecting the alkalinity. However, in reality, you cannot lower or raise one without it affecting the other. 

For any questions about water quality, or what water testing kits we offer, do not hesitate to contact our world-class team at Atlas Scientific

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