if i mix up a new batch of water in my trusty orange home depot bucket and then let it set, pump running, for a few days, it ends up growing this yellow film that will start to turn brown over a few days. it builds up on the bucket and the pump. the pump usually gets the water to 84-ish. i have gotten it with reef crystals and red sea coral pro using store bought 2.5g jugs of distilled water. i have tried cleaning the bucket with hot water and white vinegar but it still pops up. what is this stuff?

It is bacteria and is completely normal. It will not hurt anything, it just coats all available surfaces.

Its your water telling you to get it the hell out of the bucket and into the tank lazy boy
Let is sit for a day max then use it up after its mixed.

Are you leaving the buckets open top? I don't think bacterial films should be showing up that soon unless the tops are open for bacteria from the air to settle on the water surface. As long as you're storing it in a 'sealed' container with circulation I don't think you should have a film. Have you checked your pump? Some pumps can leak oil so maybe put a drop of dish soap in some water with the film to test.

Funny I was just going to post a similar question. I mix about 20 gallons of SW in a Rubbermaid Brute. I keep the lid on but only heat and circulate a day prior to water changes. I noticed the brown film on the bottom of the can and a "musty" type smell when I remove the lid. I just cleaned it with a large amount of fresh water and some bleach, rinsed thouroly and let dry. Perhaps I did not need to do that.

Old thread, but in case people are looking for an answer, I've read that this is calcium carbonate buildup. Here's an RC thread about this: http://reefcentral.com/forums/showthread.php?t=1652644