My male betta was healthy and active (always building great bubble nests) until a few weeks ago when we did a complete water change in his 2.5 gallon filtered tank. We forgot to rinse the filter before putting in a new one, so the tank was cloudy for awhile, but he didn't seem to mind. We gradually got it cleaned up, but soon noticed that he hadn't built another nest and was spending most of his time sleeping in a plant near the surface. He never stopped eating. Then he started hanging in one place looking into a corner (where I had kept a mirror at an angle) and not being very responsive. Now he's very jumpy and goes straight to the bottom of the tank to hide whenever he's startled. I started fasting him 3 days ago because he seemed to be swimming funny..kinda jerky (and at that time he was staying near the top), so I thought it might be constipation or SBD. In any case, now his fins are starting to show rot and I don't know what to do. I've been doing partial water changes daily and adding aquarium salt to his tank...along with conditioner. I have not medicated him with antibiotics...there seems to be mixed recommendations on that issue. Do you think he needs a specific remedy or just continued maintenance? I've had him less than a year, but I don't know how old he was when I got him. He seems a little bulgey behind the front fins and his color has lightened a bit there, but otherwise his scales look OK (as in no white spots etc)..just the fin rot. I am desperate. I don't want to lose another fish, though my last one died of old age, I am pretty certain. Thanks for any help you can give me and my little guy.