Are Mosquito Dunks Safe for Pools?

Mosquito larvae have to develop in standing water before they become become adult mosquitoes. Even a small area where water remains for seven to 10 days can support mosquito larvae. Because pool water often stays still over long periods, mosquitoes may lay eggs in it. Mosquito dunks may be able to safely kill the mosquito larvae in the pool.

Bacteria

A mosquito dunk contains the bacterium Bacillus thiringiensis israelensis as the active ingredient. This bacterium naturally occurs in the soil and also comes in a liquid spray formulation that you can use in the garden to control mosquitoes. The Bti in mosquito dunks produces a toxin that attacks the larvae of certain insects, including mosquitoes, black flies and aquatic gnats. The toxin damages the larvae's digestive tract and eventually kills the larvae.

Application

You can obtain mosquito dunks from pet stores, garden centers, hardware stores, pool supply stores and home improvement centers. A mosquito dunk comes as a doughnut-shaped solid item that you simply immerse in the still body of water where mosquito larvae develop. Water breaks down the mosquito dunk and distributes the bacterial toxin throughout the pool, killing the mosquito larvae. One mosquito dunk treatment lasts for 30 days before you need to reapply.

Safety

Because the toxin released by Bti only attacks the larvae of certain insects, it is safe for use in pools. If you use mosquito dunks according to the product label instructions, the Bti toxin does not harm humans swimming in the pools. It also does not harm pets, birds and wildlife. In fact, Access America E-gov E-zine recommends using mosquito dunks for all sources of standing water outdoors, including pools, bird baths and fish ponds.

Efficacy

Whether mosquito dunks can effectively kill the mosquito larvae in your pool depends on its size. According to North Carolina Cooperative Extension, mosquito dunks work best in small pools 100 square feet or less in size. If you have a larger pool, proper maintenance procedures should keep it free of mosquito larvae. Chlorine prevents mosquito larvae from developing in the pool. Turning on the pool filter and aeration system also improves water circulation and keeps mosquito larvae away.