I'm new to making cider, but I just moved my 2 1 gal carboys batch to secondary carboys after 10 days of fermenting I used star san to clean everything and when moving I had a lot of head space so I topped it off with a little more cider. Than, looking at it today I seen a film on top it kinda reminded me of what it looked like when the foam you get in beginning stages but slightly oily and I am super worried about mold. Is this mold and what precautions should I make before it becomes a a really big problem?