Rainbow film

Question
There is a strange rainbow colored film on the surface of the water in my fish tank. Is this normal?

Answer
Hi Brian

Hmmmm.....no.  Sounds like some kind of oily substance.  Can't say what's it's from, maybe fish food(though I've never seen that with all the different types of fish food I've used), or did you recently have your hands/arms in the tank and had some lotion or something on your hands?  Did someone accidentally knock something into the tank?  Or, spray anything like air freshener or something like that around?  How long's the tank been set up-and how long since you've noticed it?  The point I'm making there, if it's all fairly new, it could be something on a rock or decoration.

Christy