Why circulation is the whole defense
Mosquito larvae cannot survive in moving, chlorinated water. Skimmer action alone removes most eggs from the surface before they hatch.
This is why the mosquito problem is almost never a pool problem — it is a pump problem, a breaker problem, or a vacant-house problem. Find out why the water stopped moving and the insects take care of themselves.
The places they actually breed
Pool covers holding rainwater on top. This is the most common source in a well-kept backyard.
Skimmer throats and pump baskets on a system that is off, plus the standing water left in a filter tank.
Buckets, plant saucers, wheelbarrows, clogged gutters and low spots on the deck. A bottle cap of water is enough for a few dozen larvae.
Vacant and for-sale homes
An unoccupied home with a green pool is the classic Central Texas complaint call. In many cities a pool that has become a mosquito breeding site is a code violation the owner is responsible for, whether or not anyone is living there.
If you own a house you are not living in, the pump running on a timer is far cheaper than the recovery and the citations. This is exactly what vacation coverage is for.
If the water has already gone bad
Do not simply shock a green pool with larvae in it and walk away. Get circulation running first — larvae die in hours once the water is moving and chlorinated.
Dunks containing Bti are the right stop-gap for water that cannot be circulated yet, such as a pool waiting on a pump. They are targeted at larvae and safe for the pool surface.
A pool that has been dead for weeks is a green-to-clean, not a shock. The mosquito issue resolves on day one of that process; the water clarity takes longer.
