I am switching to a larger tank that I bought used. It was used for saltwater and I am doing freshwater but it was such a good deal I went ahead and did it. The tubes that go from the filter to the tank are not clear and see-thru. I mean you can see thru in some areas, and other areas there is a film or coating of something on the inside. It would be really hard to get something long and skinny and go in and scrape it clean. Does anyone know what this may be? I don't want it to hurt my babies once I get them in there.