Hi Melissa, I don't think the film you've seen growing on top of your starter is too worrisome or standing in the way of fermentation, but I would encourage you to cover your starter more securely to prevent it from drying out on top, which will also eliminate the film. The reason we say to "cover loosely" is not because the starter needs airflow in order to ferment properly (it doesn't), but because fermentation gases can build up in a tightly lidded container and cause the lid to pop off. It's fine to cover your starter container with plastic wrap or even the lid, as long as there is sufficient head room above the starter for gases to collect, and you open the jar now and then to vent the gases. I hope this helps! Let us know how it goes. 

Barb

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