I don't see how cycling or not cycling the tank would make a difference. While there are presumably less ammonia-consuming bacteria in a planted tank than a non planted one, they aren't completely absent. The nitrogen cycle is finished, you've just got plants competing with bacteria for ammonia.
The whole purpose of cycling the tank is so when you add fish, there are already organisms present that will consume all the ammonia. It doesn't matter what they are.
The film seems to develop in any tank with organic matter in it, so I think it might be from decomposition. Are there fish in the tank yet? I've got it in my 4.5 gallon with just plants, but adding more surface movement reduced it.
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