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How to Kill Mosquito Larvae in Swimming Pools

Going a week without using, cleaning and chlorinating your swimming pool may not seem like a serious offense. Pool water neglected for that amount of time, however, is standing water and a bull's-eye for mosquitoes looking for a place to breed and lay eggs. Mosquito larvae hatch from the eggs mature and begin biting in as little as one week. . Two commercially available products safely kill mosquito larvae in swimming pools.

Warning

Although one of these products is organic and often used on edible plants, neither is meant to treat a swimming pool in active use.

Methoprene Granules

Non-organic methoprene granules contain a synthetic growth hormone inhibitor that prevents mosquito larvae from developing into adults. In standing water, a single application remains effective for as long as 30 days.

How to Apply

Before applying methoprene granules to a swimming pool, determine the surface area of the swimming pool by multiplying its length and width. A 20-by-30-foot pool, for example, has 600 square feet of surface area.

The manufacturer of one methoprene product recommends sprinkling 1 tablespoon of the product's granules for every 150 square feet of surface area for water fewer than 2 feet deep. To determine the amount to use based on a pool's volume, figure that 4 gallons of water are in each 2 feet of water depth, and multiply that amount by the pool's number of square feet of surface area to find the pool's volume.

Treating a 600-square-foot pool holding fewer than 2 feet of water requires 4 tablespoons, or 1/4 cup, of that manufacturer's methoprene granules. If the same pool were filled with 6 feet of water, it would require three times that amount. That equates to 12 tablespoons, or 3/4 cup.

Dress for Safety

Wear protective clothing, safety goggles and chemical-proof gloves when handling methoprene so it doesn't irritate your skin or eyes.

Measure

Measure the correct amount of methoprene granules with a plastic measuring spoon or cup you don't need for any other purpose.

Tip

When you're finished treating the pool, label the plastic measuring spoon or cup "For methoprene only" with adhesive-backed tape and a permanent marker.

Treat the Pool

Sprinkle the measured methoprene granules evenly over the swimming pool water's surface.

Clean Up

Remove your protective clothing, wash yourself thoroughly with soap and water and launder the clothes separately from other laundry.

Bti Dunks

Luckily for homeowners, dunking mosquito larvae doesn't require holding them underwater while they drown. Organic Bti -- Bacillus thuringiensis subspecies israelensis -- dunks are small, bacteria-and crystal-infused briquettes that float on the water's surface. After eating the slowly dissolving bacterial spores and crystals, the larvae die from gut poisoning within about 12 hours.

One brand formulates each of its Bti dunks to cover 100 square feet of water, regardless of the water's depth. They remain effective for up to 30 days.

Tip

To keep doughnut-shaped dunks evenly distributed on the water's surface, anchor them with string looped through their center holes and weighted with small stones.

Warning

Wear the same protective clothing you'd use when handling methoprene when handling Bti, and include a respiratory mask so you don't inhale its mildly irritating dust.

Prevention of Future Problems

Having your swimming pool out of commission while you kill mosquito larvae isn't enjoyable. To make your pool's first infestation its last, clean the pool thoroughly on a regular basis, and cover it securely before an extended inactive period.

Warning

A swimming pool cover allowed to collect water is as much at risk of a mosquito larvae infestation as the pool. Drain the cover frequently.

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