First of all thank you for letting me join this forum. I’m very new to the hobby. I have set up 2 29 gallon tanks. I went away for 2 weeks and was allowing them to cycle. One has a lid and the other doesn’t. When I got home, the one without the lid has a film covering the top of the water. Some suggestions were putting a paper towel over it and it would soak it up. Not working. Please advise!