I have a 130 gallon freshwater tank and over the last 2 days the tank has become cloudy and a opaque film is covering the gravel and some of the other things in the tank. Some of my fish have cloudy eyes and there fins are begining look frayed and they are very lethargic. The levels in the tank are ammonia 0, pH 7.2, Nitrate 5ppm., Nitrite 0. I have performed two 40% water changes and added salt (1 tbs per 5 gallon changed). In the past four days I have lost 1 8in bala, 1 6in angel, 1 14in fire eel, 1 farlowela, and my other bala dosn't look so hot. The small fish in the tank seem to be doing fine. The fish seem to have labored breathing for the few minutes before they die. I have no idea what to do the cloudy water keeps coming back and the fish are going fast. any advice will be greatlly appreciated. thank you.