i think you are fighting a battle you cannot win.not sure about were you live but in louisiana if you did get them all out of the water they would be back within a few days are weeks.frog's will find your water again,just the way things go.i will assume since you have tadpoles now it must not be that must different were you live.not sure if shrimp will eat them?what are you raisin shrimp for?how big is your pond?