I have a bucket that I have been recycling lots of old rotten microbe-rich liquids into for a couple years now. Last year I had an aquarium pump running in it and it was awesome - can't wait for my new solar-powered aquarium pump so I can get back to it. I put lots of things in here: compost tea, urine, settled yogurt (for lactobaccilus?), mycorrhizal powder, etc.
Usually I keep it covered so bugs or lizards don't fall in - had this happen too many times. Now there is a film of RED something-or-other on the top. When I mix it up or pour something in it the red film disperses. Should I be concerned about this particular red film?
Other than that my microbe tea works wonders. I use it as a fertilizer and for soaking and inoculating seeds before planting.
A red film forming is not always a bad thing, certain microbes and algae have a red tint when they bloom. Most likely that is what you are seeing.
If you are concerned, then simply wait till your batch is done and when you use it, wash the bucket with vinegar/salt, that will clean it without putting anything harmful (soaps) into your container.