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Why Did My Pool Turn Green After I Put Algaecide in It?

Green pool water is something that many pool owners will face at some point in their pool maintenance and is the result of algae growing in the pool along the walls and bottom of the water. Algaecide is one way to prevent algae, but sometimes once the onset of algae has begun, it can still fight off the chemicals in most common algaecides.

Green Algae

Green algae is one of many forms of algae that can develop on your pool surface. Luckily green algae, the more common of the algae forms, is also the easier of the algae types to kill. Most cases of green pool water develop slowly due to a lack of sanitizing and pool maintenance. In some cases, however, algae is known to appear almost overnight in perfectly sanitized pools as well. The earlier you attempt to kill the green algae, the easier it will be.


The use of algaecides is debated among many pool professionals. One thing agreed upon, however, is that the use of an algaecide product is most effective in the prevention of algae rather than the treatment of it. The same way water can sometimes turn green in a perfectly sanitized pool, it can also turn green seemingly with no explanation after adding algaecide as well. The algae may have formed after adding algaecide because the algae blooms had already began to form and were capable of blooming despite the addition of algaecide.


Algaecide can be added in conjunction with a chlorine shock treatment for chlorine-based or salt water pools. The primary remedy for the green pool water is not the algaecide but rather the shock. Pool owners use shock to quickly elevate the level of chlorine in their water for the sole purposes of killing bacteria and clearing the water. Scrub the pool walls, bottom and any accessories prior to adding the shock treatment. Shocking the pool more than once to completely kill the algae may be necessary, putting your pool out of commission for a few days.


Properly balancing your water chemistry and keeping your pool sanitized is a good way to prevent algae growth in your pool. Never allow your pool to become cloudy as this is the first step in facilitating the growth of algae. Use algaecides as a part of your regular water maintenance schedule to stay ahead of the curve. The dosage of algaecide will vary based on your pool size. Adding too much can stain liners and cause suds and bubbles on our pool surface.

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