with 2 of them, i would try at the 25% setting. i like water flow, and lots of filtration, but you must meet the needs of the fish. if the filters are blowing the fish all over the tank, and they cant find a space to rest, thats a problem. id start 25% on each, and if that doesnt seem to be enough, turn one up to 50, if still not enough turn the other up to 50 too, repeat as needed.