I've had similar problems. Did you use spring water when you filled the water area? It could be due to your water quality in your area.
Sometimes if water just sits for a bit without any movement, something from inside the water just floats up to the top to form a powdery film on the top of the water. I don't know if it's contaminants or microorganisms or what. But I do know that if you change the water for spring water and/or add a little movement, it will usually solve the problem.
Also, do you have anything touching the water? Sometimes if some driftwood, moss, or dirt is touching the water it can make it do wierd things like that. When I have a built-in water area, I always make it so that gravel is the only thing the water can touch. You can see the water line through the wall of the aquarium, does the water line ever touch anything other than gravel?
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1.1.0 Sunburst Veileds (Oscar and Lizzie)
1.1.0 Azureus darts
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