A solar pool cover’s primary function is to capture solar energy and transfer it to the water, while simultaneously acting as a barrier to prevent heat loss and water evaporation. While a solar cover is not the direct cause of an algae bloom, it creates conditions that greatly accelerate the growth of existing algae spores if the pool’s chemical balance is not precisely managed. The misconception that the cover itself is the culprit stems from the fact that its heat-retaining and sealing properties intensify the environmental factors algae need to thrive. Therefore, understanding how the cover facilitates this growth is the first step in preventing an outbreak.
How Solar Covers Create Ideal Algae Conditions
The most significant way a solar cover encourages algae is through elevated water temperature. A cover can increase pool temperature by several degrees, often pushing the water above 84°F, which is a threshold for pool chemistry. Warmer water provides an optimal breeding ground for algae, allowing it to multiply at a much faster rate than in cooler conditions. This increase in temperature also accelerates the consumption of free chlorine, the pool’s primary sanitizer, which means chlorine levels drop quickly.
The physical presence of the cover also hinders the natural processes that keep water healthy. By sealing the water’s surface, the cover restricts gas exchange, which is the water’s ability to “breathe.” This reduced aeration can affect the water’s sanitizing power. Furthermore, when the cover is left on for extended periods, it often leads to reduced pump and filter run times, minimizing water circulation and creating stagnant areas where algae spores can settle and grow undisturbed.
Algae’s Primary Drivers: The Role of Pool Chemistry
Inadequate water chemistry is the foundation of an algae outbreak, with low chlorine being the single greatest factor. Even a small decrease in free chlorine is magnified by the warm water under the cover, as the sanitizer is consumed rapidly, sometimes having its effectiveness cut in half above 84°F. Algae can become resistant to low levels of chlorine, allowing a small drop in sanitizer concentration to quickly turn into a full-scale bloom.
The pool’s pH level also plays a major part in chlorine efficiency. Chlorine is most effective in a slightly acidic environment, typically between 7.2 and 7.6. If the pH drifts higher, becoming more alkaline, the active form of chlorine decreases significantly, rendering the remaining chlorine less potent against algae. This vulnerability, combined with the heat-driven chlorine loss, creates a perfect storm for algae growth.
Algae also require a food source, which comes in the form of nutrients like phosphates and nitrates. These nutrients are introduced by organic debris, such as leaves, rain, or runoff, which the solar cover can trap. If the cover is not cleaned or if debris is left on the water’s surface, the trapped nutrients feed the algae, allowing it to flourish rapidly once the chlorine level dips. Removing these nutrients is an important step in starving the algae.
Essential Maintenance When Using a Pool Cover
To counteract the environmental changes caused by the cover, pool owners must adopt a rigorous testing and maintenance schedule. Water chemistry should be tested daily, especially during peak summer temperatures. This ensures free chlorine levels are consistently maintained at a slightly higher range than usual to keep pace with the accelerated consumption rate caused by heat.
Increasing the pool’s circulation prevents stagnant water under the cover. Running the filtration pump for longer periods, particularly during the hottest part of the day, helps distribute the sanitizer evenly. This prevents the formation of “dead spots” where chlorine cannot reach and algae can take hold.
It is beneficial to remove the cover completely for a period each day to allow the water to “gas off” and aerate, which helps stabilize the chemistry. The cover itself needs periodic cleaning with a soft brush and water to remove accumulated debris, dirt, or algae spores clinging to the underside or top surface. When super-chlorinating or “shocking” the pool, the solar cover must be removed until chemical levels return to a safe range, preventing damage to the cover material and allowing the treatment to be fully effective.