I have a divided 10g and there is like a film on the top of one side that looks like oily. Its hard to explain. When I drop a pellet in there, the film separates. It is so weird. It hasnt even been sitting for a long time, I just messed around with the water yesterday installing a new divider. And it can't be because of the water not flowing through the divider because even before when I had a different divider, it was full of holes and very open and the film was there. It isn't dirty either. The tank is about a month old. But it is used. I rinsed it out with hot water and salt and vinegar too. Even the other side of the divider has a little film on it. I am just concerned that my fish can't breath through it. Sorry for the novel. What do you think it is/I should do?