I have only had my betta a week..He is a male crowntail. He is living in a 10 gallon tank with plastic plants, rocks, gravel, ornaments for hiding and a real plant. There isn't a filter, but he has a heater the temperature is constantly at 78 degrees. I have ordered a light off the internet, but at the moment he just has daylight/normal light in the room and dark over night. I washed the tank and everything else in really hot water before anything. The water stood for 24 hours and was heated to proper temperature and had a tiny bit of aquarium salt and the right amount of water conditioner in it, before I put him in. He was super perky right up until yesterday, swam around a lot and would come right up to the top when you put food in, or up to your fingers if you went to pull out a bit of plant. He would eat straight away, although with the pellets just seemed to eat and then spit it out several times, but i figured thats because they are too big for him and he just took something from the edges. He also had a few dried bloodworms a day. I would only leave the food in there for a minute or so and then take any leftover out. So yeah, he seemed very happy, swum about lots, eating, resting in the plant, flaring if i held a mirror up.
But as of yesterday he doesnt seem happy. He just hangs out at the top of the tank, just floating there. And even if I drop food in front of him he just ignores it. He will move a little bit, does change positions, but always just by the surface. The tank did develop a thin clear film over the top, but it is easy broken when he goes to the surface, and I looked online and it seems common, I used kitchen paper on the surface of the water and it got rid of it, but my fish didn't even move while I was doing that. He looks all kind of clamped together, his tail isnt really spread out anymore, but I cannot see any damage or rot or wounds or fungus, he just seems lethargic and doesnt want to eat.
Does anyone have any ideas what is wrong and what I could do?
Thankyou for taking the time to read this, and I hope I can do something and he will be OK.