fungus growth

Question
I have 1 betta in a 1.5 gallon tank with filter. I use tetrabetta pellet food for my betta. Un-eaten pellets do not break down, sit on the gravel, and form what looks like a scum around them. I have noticed a film forming on the surface of the water. I have done a water change and cleaning, but my betta is now acting extremely lethargic. No change in appearance can be detected. What can I do?

Answer
Mike,
Firstly, the 1.5 tank is not big enough for him. He should be in nothing less than 2.5 where 5 gallons is best. When you feed him, he should only get 1 to 2 pellets a day. His stomach is the size of his eye so he cannot eat too much. If after 2 minutes he has not eaten all the food, it needs to be removed. If you do not remove it, you will experience everything you are now. As for the filter, he does not like them nor does he need them. Betta's have an organ call a labyrinth organ. This allows him to go to the surface of the water and get air. In that small of a tank it is definitely not needed. He is, however, a tropical fish and needs a heater in his tank set to 80 degrees at all times. This is one of the reasons he needs a bigger tank. You will not find a heater to fit that small tank, that will keep the water at the right temperature. What I would do now is do a complete water change and clean his gravel.  If you do all the following for him, you should see a difference in him.

1. Get him a bigger home
2. remove the filter
3. add a heater
4. remember to do weekly water changes.

He is becoming lethargic because his water is too cold. Once you get his water to the right temperature, you will see a huge change is his activity.