How did my betta die and how can I keep my other bettas from getting sick?

I had a very happy active betta fish. Yesterday I noticed some white cotton like stuff on him in a couple different areas. I changed his water, added a little aquarium salt and put in a dose of Jungle fungus clear in his water. This morning he was dead. He had cotton like white patches all over him, including his eyes and had what looked like a halo of white all around him. What killed him? Was it fungus or something else? Maybe flexibacter? If so what should I have done to help him and what medicines work? I have two other betta fish, one male and one female. I don't want them to get sick as well. I'm worried they will have caught it from using the same net or other equipment. I use a turkey baster to suck up any uneaten food or feces out of their bowl. I rinse it off with hot water in between using it on different bowls. How long does it take for bacteria or fungus to die on a net or the baster or the empty fish bowl I now have. Should I disinfect them? OR will that kill the fish?