What is Swimming Pool Alkalinity?

The Short, Short Version

Swimming Pool alkalinity (often called total alkalinity) is a measurement of the concentration of alkaline materials in your pool. Alkaline materials stabilize pH but buffer chlorine sanitation.

How do Alkaline Materials Enter Pools?

Pool stabilizer is the most common way alkaline materials enter a pool or hot tub. Cyanuric acid – the active ingredient of pool stabilizer – is an alkaline material that buffers pool water. There are two outcomes of buffering: 1) pool pH level is stabilized against acidic contaminants and 2) the sanitizing power of free chlorine is diluted.

What are the Benefits of Maintaining Pool Alkalinity?

Maintaining a pool alkalinity between 80 and 120 ppm has several key benefits. The most important is that your pool pH level is stabilized. Low pool pH level may result in corrosion of your pool surface and pool tools, such as your pool filter. High pH will dramatically reduce the free chlorine’s ability to sanitize your pool’s contaminants.
Balanced pool alkalinity will make it much easier to keep your pool pH level in a tight range, thereby reducing the possibility of corrosion and the ineffectiveness of free chlorine.

What are the Downsides of Pool Alkalinity?

Like most things, pool alkalinity is not without its drawbacks. The greatest drawbacks come from not maintaining total alkalinity in the recommended ranges. When there is too little alkalinity, pool water is prone to oscillate between acidic and basic. Acidic pool water increases the effectiveness of free chlorine’s sanitizing ability but may cause corrosion. Basic pool water can dramatically reduce free chlorine’s sanitizing ability.
Still, even when total alkalinity is properly maintained, it can cause issues. The most apparent issue is the effect it has on chlorine sanitation. By buffering pool water to maintain a pH level between 7.4 and 7.6, alkalinity reduces the effectiveness of chlorine sanitizer. However, the benefits of pool alkalinity tend to far outweigh the costs. Most pool owners find it is well worth it to maintain proper levels of total alkalinity.

What Should Total Alkalinity Be in Pools and Hot Tubs?

Total alkalinity is a measure of the concentration of alkaline materials in pool and spa water. The most common alkaline material is cyanuric acid, commonly referred to as pool stabilizer. Fundamentally, alkaline materials buffer pH levels and combat the acidic effects of many common contaminants found in pool and spa water, such as urine.
It is important to remember that buffers – such as cyanuric acid and other alkaline materials – also inhibit free chlorine from sanitizing pool water to some extent. This is a much greater concern with hot tubs than it is with swimming pools. Hot tubs experience a higher concentration of swimmers and therefore a higher concentration of contaminants. If hot tub water is buffered too much, free chlorine will be ineffective against folliculitis (i.e. hot tub itch).
The recommended total alkalinity for swimming pools is between 80 and 120 ppm. Many pool professionals recommend an exact level of 90 ppm. The recommended total alkalinity for hot tubs is 50 to 80 ppm. These ranges ensure stable pH levels while not buffering water too much to render free chlorine ineffective against common contaminants.

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