I have been keeping Betta fish for a number of years, and have never experienced anything like what has happened this past week!
One of my old timers (3 y/o) was really failing, and I chose to euthanize rather than watch him suffer. :( I cleaned his tank with warm water, and got a new guy at Petco. Within a few days, his fins were clamped and he was head-down at the bottom. I thought maybe he was cold (I have never heated my tanks, as they seem to stay around 75 on their own), so I went back to Petco and got an 8W automatic heater. Initially, he perked up...but by the next day, his fins were shriveling and rimmed with white. He was gasping for air, lying on his side. A few hours later, he was dead, covered in stringy white stuff. :(
I took him back to Petco, and brought home his replacement. New guy did fantastic for the first day, but by the second was also lying on his side gasping, fins clamped. Hard to tell if there's white stuff, since he's a pale green dragon. I unplugged the heater last night, and today he is moving around more but still clamped and wanting to rest on the bottom.
Notes: Between 1st and 2nd fish, I disinfected the 1 gal tank and everything in it, using HOT water and vinegar. I always use fresh distilled water for water changes.
I can't imagine what's going on here, except that perhaps I have a defective heater that is getting too hot? The temp on my strip thermometer read 84-85 when 2nd fish was at his worst, but maybe that is not accurate? Am I dealing with some kind of latent infection brought on by the stress of moving, or is my heater killing my fish?
Oddly, I have the same type of heater in my other (identical) tank, and that fish is thriving.
What is going on here, and what else should I do??? I would love to save my pretty green dragon if I can...
Thanks in advance for any insights! Sorry this is so long!