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How to reduce pool alkalinity and keep pool pH low

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How to reduce pool alkalinity and keep pool pH low
09/04/25

Knowing how to reduce pool alkalinity and keep pool pH low is key for clean and safety reasons, and is part of ensuring bathers’ experiences are always safe and pleasant. As such, it is a key aspect of pool operations and one that should be addressed proactively, rather than after issues arise.

Alkalinity or total alkalinity refers to the measurement of the alkaline salts within the water and their ability to neutralise acids. Controlling alkalinity is important because it prevents sudden pH changes, which is key to ensuring effective chlorine disinfection. In other words, total alkalinity refers to the ability of the pool water to resist pH change, and thus ensure correct functioning of equipment.

Let’s take a look at the most common questions around how to reduce pool alkalinity and keep pH low, and the most efficient ways to tackle issues related to pH levels.

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    The FAQs about pool alkalinity, answered

    What causes high alkalinity?

    The recommended range for a swimming pool’s total alkalinity is between 100 and 150 ppm. When a substance and other pool chemicals are added to pool water, total alkalinity will react to keep the pH in the desired range (7.2 – 7.8).

    There are several factors that can alter alkalinity. Among them are:

    • Changes in the volume of water due to evaporation, which causes a concentration of calcium carbonate.
    • Lotions, sun creams, sweat and residues.
    • Contact with carbonate rocks.
    • Incorrect use of chemical products.
    • Malfunctions in the pool filtering system.

    What happens if pool alkalinity is too high?

    If the value is higher than 150 ppm, water can become cloudy and the pH will drift upward. When the total alkalinity value is less than 100 ppm, pH levels may become unstable.

    In fact, high alkalinity can have a number of undesirable consequences, including:

    • An uncontrolled increase in pH
    • The cloudy water phenomenon
    • Irritation in the eyes, throat and ears
    • Scaling on walls and pool accessories
    • With high pH, the effectiveness of chlorine and other disinfectant treatments decreases

    How do I lower the alkalinity in my pool fast?

    One way to reduce alkalinity is to add acidic compounds and pH reducers. Generally, the acidic properties of these products react with the carbonated or bicarbonate alkalinity to produce carbon dioxide, expelling the carbon responsible for the high alkalinity in the form of gas. These come in liquid, powder or tablet formats.

    Once the alkalinity level begins to stabilise, it will take 48 hours to rebalance the pH levels of the pool.

    Similarly, hydrochloric acid is highly recommended to reduce pool alkalinity quickly and effectively.

    When it comes to fixing issues related to calcium carbonate scale, it can be removed with weak acid solutions, such as acetic acid. The pool should be empty during this procedure.

    How to correct low alkalinity

    The correction of low alkalinity is a bit more complicated, as it may cause pool pH levels to fluctuate. It’s usually caused by malfunction of the pool filtration systems or lack of adequate maintenance. For example, trichloroisocyanuric acid tablets can make the water too acidic.

    Low alkalinity and unstable pH levels cause corrosion and stains on fittings and metal parts, stress on filtering systems, irritation of eyes, nose, throat and skin, and inefficient disinfection. If the pool pH is low, green water may also appear.

    Unlike in cases where the alkalinity tends to increase, a decrease in alkalinity requires much greater precision. It is recommended to calculate the volume of water in the pool and the pH at the time of maintenance. Then, apply an alkalinity increaser, usually sodium bicarbonate. Following the dosage indications will be essential to achieving the desired results.

    Beyond corrective measures: the role of automatic control solutions in how to reduce pool alkalinity

    If you’re wondering how to reduce pool alkalinity, you might be interested in going beyond corrective measures and ensuring the right balance in pH levels is always achieved.

    This is where automatic control systems come in. Designed to control large commercial or public pool facilities, these solutions maintain the optimal water pH parameters, making maintenance more efficient and sustainable offering peace of mind for operators.

    As pool engineering experts, at Fluidra we offer the following three solutions to ensure pH levels are well balanced:

    • AP PR Series is the professional choice for control and dosing. The integrated panels based on controllers provide the best authentically ‘“Plug & Play” solution, pre-assembled on a panel to control pH, ORP and free chlorine in the water.
    • Guardian Pool combines traditional control and dosing elements with total digital control of its values. This facilitates the management of the pool parameters, as well as the ability to analyse or detect possible errors with historic data.

    These systems represent cutting-edge solutions for managing alkalinity and pH levels beyond reacting to issues, ensuring bathers are always protected and have an enjoyable experience. As such, they can be understood as not only solutions for keeping pool pH low, but as part of a wider move towards automatic operation in pools that guarantee optimal conditions at all times.