When I make my saltwater I let it mix for a couple of days in a black garbage can. When I pull out the power heads they are covered in a film .It is also on the sides of the garbage cans. I use a Ro unit . I'm not sure what it is. The best way to put it is if you didn't clean your bath tub for a year the ring of scum that builds up is what it looks like in the garbage can and on the power heads. What do you think it can be

