can anybody please advise me as to what to do with my tank please.i have a very thin film over the top of the water.the fish are coming up for air and the water is not moving,i have scraped it with my net the best i could and it's still there.the bubbles are gathering and not moving.it's very cloudy just at the top.do i do a partcial or full water change?i dont want to loose any of my fish help is needed thanks