Slime on Water Surface

Question
I've had a male betta in a one-gallon bowl for about a year now, no problems.  Within the last couple months, a thin but resiliant layer of clear "slime" has formed gradually after each water change.  I swap the water out entirely, rinse the poor guy off, and clean the bowl thoroughly each time, but this stuff just keeps coming back.  My fish has learned to poke through the layer and create a hole to better access his food, and it doesn't seem to be affecting him adversely.  I went to my local betta store and they said that the fish itself was creating it.  I do typically add a bowl conditioner/stress coat to tap water, but I have tried bottled water and still the problem persists.  What is it?

Answer
Hi Julie;

Some bettas do seem to create an "oil slick" on their tank water via their waste. It is probably from his food, even if it doesn't look or feel oily itself. He may not be digesting the oils and they are coming out with his waste and floating on top. If you have been using a pellet, try frozen bloodworms or shrimp instead. A few chunks of green peas popped from their little round shells two or three times a week is good for his digestion too.

It really isn't healthy for him to be physically rinsed off. It removes his protective slime coating that protects him from injury, parasites and disease. I know you probably think it could be responsible for the oily film, but the slime coating is not oil-based. It is "mucosa" and generally tends to sink downward or totally dissolve.

If the film continues in spite of diet changes you might consider putting in a small filter that runs with bubbles or getting him a bigger tank with a slow-flow filter. Agitating the surface of the water usually totally eliminates this problem.

Good luck...

At Your Service;
Chris Robbins