I've been trying to fight the fin rot in my veiltail Psusennes' anal fin for a month now. I think I've gotten some handle on the major tank issues that have come up, but he is still losing fin and has become a bit twitchy and lethargic over the weekend.
He is one of 2 bettas in a divided 5.5 gallon tank with a Whisper 10i filter and 25W heater, both of which are on his side of the tank. The other betta Ramesses is a bit lethargic as well, but he was never as active as Psusennes so this is less concerning.
Water temperature is steady at 80 and all water changes are safely within 2 degrees of that. I have had the water tested at the local fish store twice the last month. The first test apparently did not have enough water to test ammonia, but the carbonates were apparently off the chart; this is very odd since the local tap water I use is less than 10ppm. This was resolved by the next test a week later. I spent that week doing small 10% changes every second day after working a dose of aq salt into the tank over the course of several hours and changing the filter media. More aq salt was added as needed during those changes
On the second test, carbonates were back below 10ppm, pH was around 6 as it had been before, but ammonia was at 4.9 so I was very worried. I couldn't think of the source as there are only the 2 fish in this bare bottomed tank with only plastic plants and river rocks. I finally think I found the source though: the current from the filter was too strong so I had a sponge placed there as a baffle. I thought there might have been some of my beneficial bacteria living in there so I forgot to rinse it regularly. I did so on Saturday, using water treated with Stress Coat so that I wouldn't kill off any beneficial bacteria (my water conditioner) and it took 3 jugs of water to finally get all the gunk out. I was quite horrified to realize this, especially since the poor boy lives on the side where water was coming out past that. No wonder he got sick!
I'm planning to do another 20% change tonight minimum, but I would definitely appreciate any advice on the matter. I usually change 30-50% per week with Stress Coat. My boys are fed 2-3 pellets in the morning and 3 pellets in the evening, except for their weekly fast day. The ill boy has been with me for about a year and a half and, outside of some tail biting, this is the first time he has been sick.