What can I do about my fish tank scum?

Is your filter working? When I had a fish tank I not only scrubbed abd rinsed the tank, but I rinsed the rocks and any of that decorative crap in there. Dust sometimes settles on top of the water if you don't have a lid or screen. I would suggest purified water. Also, in the future, after you replace the water make sure you put a few drops of de-chlorinating solution in there. That may have killed your fish. I also let the water settle and warm up before putting them back.