The fact that you are providing agitation to the water will prevent any female mosquitoes from trying to lay their eggs there. They will not try to lay eggs in moving water, even slightly moving water. Mosquitoes like standing and very quiet water that has some nutrients in it.
Stagnant water will go bad, just like milk, only not as quickly. Once the bacteria builds up, "momma mosquito" somehow knows this is a good spot for her babies. Some like brackish water (Oc. sollicitans), some like fresh floodwater (Ae. vexans, Ps columbaie, Ps. ferox) some like relatively clean container water (Ae. albopictus) and some like absolutely filthy stinking container water, like catch basins, sewers, and water treatment plants (Cx. pipiens). There is one mosquito that can lay it eggs in slightly moving streams, An. walkeri, I think, but I don't think it's found in your area......
As far as the dunks go, the fish will probably just eat them. Not to worry, BTI is harmless to aquatics, plus with that amount of fish in there, there's no way the larvae can survive.





