Natural mosquito killer for standing water?

Summit Mosquito Dunks are suppose to be good. I use bleach.

If you don’t chlorinate your pool, Mosquito fish are an option. If you don’t have a lot of mosquitos, you will likely have to supplement their diet.

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What a great question. Cutting down on mosquito’s is always a considerate thing to do!

A few drops of dish detergent will break the surface tension the larvae need to breathe. They cannot attach to the surface and fall to the bottom. You need to apply it regularly.
Vegetable oil works too but is messy.

I use these in my rainwater collector. For something a little less direct, you may want a bat- or bird-house for species that nom on mosquitoes, too.