is this their first time with distilled water? distilled water is devoid of any minerals that the frogs actually need. your best bet would be to use tap water that has been dechlorinated. i can tell you your pH, it's 7.0. distilled water is neutral in every way. no minerals, means nothing to buffer the pH to. i wouldn't believe that the sound of rushing water would disturb them. bullfrogs are found near streams as well as ponds and lakes. they may even actually like it. the increased flow will also disperse the film on the top of the water for you.
as far as their color, maybe they are still acclimating to a new environment. much like you or i would if we were suddenly moved from our homes.
