White Film in water (Betta Fish)

Question
I have had this fish for over a year in the same "tank." I recently noticed a white film keeps reappearing at the surface. I noticed someone else posted about it and read your suggestions. I HAVE noticed my Betta is acting a bit "limp" or tired these days but when he/it/she sees food she goes crazy so she does spark up to life again.
Anyway I did rinse out the tank and wipe it down and I use distilled bottled water as per the suggestions on the instructions that came w/the fish.
What now?
Thanks

Answer
Hi Sara,
Let me just start out by saying that distilled water is not a good option for any fish. Distilled water has no minerals or electrolytes in it, and therefore eventually your fish will suffer from malnutrition. Switch to tap water and use a dechlorinator.
Does this white film resemble an oil slick? If so, that's exactly what it is. You can remove it by floating a piece of paper towel at the top and removing the oil.
If it is truly just a white film, then it seems there is something in your water that should not be there. Do you use any specific chemicals in your water, or perhaps have lotion on your hands when you are touching the water for any reason? You'll have to find the source and get rid of it.