betta, siamese fighting fish

Question
Hi,
I have had a siamese fighting fish for about five months, and he lives in a fish bowl about eight inches in diameter.  I don't have a filter and I don't know the pH, or ammonia/nitrite levels.  I try to change the water weekly.  However, within the last month despite changing the water, a thin film keeps forming on the top layer of the water.  I haven't changed anything about the tank, and I was wondering what this film might be caused by?  I am not sure how to get rid of it, and I am afraid it might be harmful to the fish.  Have you ever heard of something like this?
Thanks,
Emily

Answer
Hi Emily;

It's probably just oils from your fish's body or from maybe his food. Some bettas have that "oil slick" on their water and some don't. It doesn't seem to be harmful to them. To get rid of the layer of oil it does help to agitate the water with a little air stone hooked to a very small air pump. I know that isn't exactly what you signed up for in keeping a betta but it does help the water stay cleaner-looking in general too. Or, just get him a small tank with a slow flowing filter. There are some very nice little systems under 5 gallons with a light and filter that are really easy to keep clean. In a filtered little tank just change 25% to 50% of the water once a week and and it stays pretty nice.

At Your Service;
Chris Robbins