Using Algaecide in Swimming Pools

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Using algaecide in swimming pools is an effective way to prevent and control the growth of algae. Algaecide is a chemical treatment that kills and prevents the growth of algae in the pool water. It works by disrupting the algae’s ability to photosynthesize, ultimately killing it.

To use algaecide in your swimming pool, follow these steps:

1. Test the water: Use a pool testing kit to check the pH and chlorine levels in the pool water.

2. Clean the pool: Remove any debris or leaves from the pool and brush the walls and floor to remove any existing algae.

3. Add algaecide: Follow the manufacturer’s instructions to determine the appropriate dosage of algaecide for your pool size. Add the algaecide to the pool water, distributing it evenly.

4. Run the pump and filter: Turn on the pool pump and filter system to circulate the water and distribute the algaecide throughout the pool.

5. Monitor and maintain: Regularly test the pool water and adjust the pH and chlorine levels as needed. Reapply algaecide as necessary to prevent algae growth.

By using algaecide as part of your pool maintenance routine, you can keep your swimming pool clear and free of algae, ensuring a clean and enjoyable swimming experience.


Algae are almost inevitable in pool water. The most common type is green algae, which can turn the water green and cloudy in heavy rain, if introduced by a contaminated swimsuit, or if the pool chemicals are not properly balanced. Yellow (mustard) algae and black algae can also discolor the water, but they tend to form clumps and attach to pool surfaces, making them more difficult to eliminate.

The most effective algaecides for pools usually contain copper compounds, although the exact reason for their effectiveness is somewhat of a mystery. However, they do work, although they may not always be necessary. Chlorine is actually a more effective method for controlling green algae than algaecide, although using algaecide alongside chlorine won’t cause any harm. If you are dealing with yellow or black algae, getting rid of them can be a challenging task.

Adjusting pH to Support Chlorination

If you wake up one day and notice a green tint in your clear pool water, it is a clear sign that the chlorine is not disinfecting as effectively as it should. This could be due to insufficient chlorine concentration, or it could be caused by an imbalanced pH level. The pH should ideally be between 7.3 and 7.6, and any level higher or lower than that will inhibit the sanitizing effect of chlorine.

The first step in eliminating algae is to adjust the pH level. If the pH is too high, you can add muriatic acid to lower it, and if it is too low, you can add baking soda or soda ash to raise it. Once the pH stabilizes at the correct level, you can proceed to the next step, which is shocking the pool to significantly increase the chlorine concentration to above the recommended value of 3 parts per million (ppm). The easiest way to do this is by adding a pool shock treatment, typically 1 pound per 10,000 gallons of pool water, but make sure to check the product label for specific instructions.

Add Algaecide After Shock Treatment

If you notice that the green discoloration in your pool water has disappeared after shocking, adding algaecide may not be necessary. However, it won’t cause any harm and can be beneficial if the discoloration persists. Wait for the pH level to drop to a safe level for swimming (3 ppm or below) and then add an algaecide product, such as Pool Time Algicide + Clarifier, following the recommended dosage provided in the product instructions.

Add the algaecide gradually while walking around the pool. The product needs time to dissolve in the water and circulate through the pool pump. As the algaecide eliminates the organisms, the pool clarifier causes their bodies to cluster together, making it easier for the pool filter to remove them. It is important to clean the filter a day or two after treatment. If the green discoloration persists, you can repeat the treatment, but be cautious not to add too much as it can cause the pool water to become foamy and irritate the skin.

Eliminating Black and Yellow Algae

Unlike green algae, black and yellow algae cannot be killed by algaecides as they are resistant to chlorine. The only way to get rid of them is by scrubbing and vacuuming. This process requires more effort. To successfully eliminate these algae, you need to scrub the affected areas, balance the pool chemicals, and scrub again. Finally, you must shock the pool with triple the normal dose and scrub once more to completely eradicate them.

Fortunately, black and yellow algae are not as common as green algae. To prevent them from appearing in the first place, it is advisable to add algaecide to the pool water regularly. Additionally, practicing proper hygiene, such as showering and cleaning swimsuits before swimming, maintaining the water chemistry, and periodically shocking the water, is essential.

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