So this is weird... I had a couple of fish die in rapid succession leaving just my betta fish in the tank (5 gallon). When I went to do a partial (75%) water change, immediately I noticed a film on top of the water. A few water changes later, the film was still there. Last weekend I did a complete water change -- put the betta in a separate bowl for the time being and thoroughly rinsed everything in his aquarium with hot water -- including the filter itself (I have one of those detachable shower heads and took advantage of it). Today I see that the film is back. When the betta was by itself (for about 6 months), there was never a film, so I'm sure it's not from the betta. What could it be? I'm thinking of putting him in a separate container for a few days and cleaning the aquarium with some form of detergent -- in which case I would rinse the aquarium out with really hot water for several sessions over the course of 2 or 3 days. What do you all think? I know we're not supposed to use detergents, but I really don't like this film and don't know what else to do.
I'm using floating pellets and he consumes each one because I only feed him as many as he will eat. I'm using gravel substrate, I have no plants, and plastic toys.
By the way, this betta seems to last forever -- he's about a year old now and is still feisty as ever!