I have finally started to get my tank ready and set up and today I am cleaning the tank out with warm salty water. I have a problem though, the tank is secondhand and there seems to be a milky film all around the top sides of the tank. I have tried to wipe over the tank and also scrub the area gently with a soft scoura but it doesnt seem to do anyhting. I have no clue of what it could be.