I did a water change out a week ago but today I noticed a thin white film on the surface of the water. The film is not uniform, it seems to be a little thicker in some places. A piece of floating food will create a little trail behind it clear of the film. There is good flow and a new charcoal filter is in place Anybody seen this before? \n\nI did add some very salty water in slow increments to bring the salinity up starting a couple days ago.