I have a 5g with only a male betta in it. Tank has been up about 2 weeks, he's been doing fine. He blew his first bubble nest yesterday. Since he made it, I've noticed a light filmy substance on the surface of the water. I'm not sure what it is. Is this a side-effect of the bubble nest, or should I investigate? It was even there after I did a water change. The only thing I can think of if it isn't the bubble nest would be the filter (it is an small internal "Whisper" filter)?