You should not need to change the water if Amdro Fire Ant Bait gets into the pool. Once wet the product breaks down and only contains a small amount of active ingredient to kill insects.
Amdro Fire Ant Bait is labeled for Argentine ants. You would sprinkle 2-5 level tablespoons of Amdro Fire Ant Bait around the mound, for normal sized mounds. . Be sure not to disturb the mound. Please see the product Label for specific rates.