This is my third betta and third bad experience! I previously lost two so tried to do everything exactly right for this guy, but it didn't matter! I love my betta. He is about 8 months old. He spent the first three months in an unfiltered one gallon tank. He acted bored and a little depressed so we purchased a 10 gallon tank for him. We bought two rosey red minnows to try to cycle the tank before we moved him into it. We didn't move him until 4 weeks after the tank was set up and ammonia read 0. He was for about two months, and then about three weeks ago he started showing signs of illness. I first noticed him sitting on the bottom of the tank in the mornings, which is normal for a betta, but not normal behavior for him. Next I noticed him sitting on top of the heater or wrapping himself around the top of the filter of the tank and trying to stay at the top. Over the next couple of days I noticed that he was darting around the tank as if something was driving him crazy, as did the other fish.
The next day one of the rosey red minnows had an eye literally explode. Neither of these fish had acted sick or had poppy eyes the day before. It literally just happened over night. Two days later I noticed our Betta had a black spot on his lip. I decided that maybe the minnow had popeye and the betta was getting a bacterial infection, so I treated with Marcyrn2. After this finished it's course I noticed that the Betta's left gill was swollen and would not shut and he began gasping for air (looking like he was yawning or drinking). I then tried Tetracycline. This medicine finished it's course three days ago. He has stopped darting around, but still has the black spot and swollen gill and still clearly cannot breathe. He does still have a good appetite but is very lethargic.
Again, he is in a 10 gallon tank that is kept between 80 and 82 degrees. The water was being changed 25% once a month, but has been changed between 25 and 50% three times in the last three weeks. The ammonia was 0 before he was put in. We purchased an ammonia monitor after we moved him into this tank, and the entire time he has been in there it has not read that the ammonia has been more than 0. We have also used the drop test kit periodically to check to make sure this is working, so I don't think it is ammonia burns. We have checked the water quality over the last three weeks and nitrate and nitrite is also 0. The pH is slightly high after water changes but we have been using pH down to correct this.
Since I know the water quality is good, I am at a loss. I considered gill flukes but he has not been scratching and the darting around the tank has stopped altogether. Also, I'm not sure where he would have picked up a parasite. I haven't read that a bacterial infection can cause swollen gills, but if it did shouldn't two antibiotic treatments have fixed this by now? I am really afraid we are going to lose him soon. If anyone has any ideas, please let me know. Yesterday I added aquarium salt and coppersafe. We have been adding beneficial bacteria since we started the tank. I would post a picture but he is dark purple and hard to see, so I don't think anything would show up. I MIGHT LOSE MY MIND SOON. HELP!