white stuff growing

[jillnjasper]

I have noticed that the tubing leading from outside the tank to the filter has started to grow some white stuff on it. My bigger concern is, though, that my fish likes to swim up against the tubing. What is this white stuff, and can it harm my fish?

[fish_4_all]

I have had that on tubing when I used it and it never seemed to hurt the fish. I think it is a slime that feeds off something in the tubing or something similar to that, eventually it went away but only after a few months.