Having trouble with betta clamped fins

[musiclover]

I've been keeping fish for a while now, but I wouldn't call myself an expert. I've had my betta for about 6 months, and she's probably around a year old. She's been dealing with mild fin rot for 2 months, and despite my best efforts, it just won't fully heal. I've increased water changes, added salt, and even tried antibiotics, but nothing seems to be working. Now she's developed clamped fins - you can see it in the pic I posted.

The 5-gallon tank is fully cycled, with zero ammonia and nitrites, and 10 nitrates - all stable with a pH of 7.8, according to my API master kit. I've been changing 1/4 to 1/3 of the water every 3 days. I was worried the tank might be too cold, but I added a second glass thermometer, and it's reading 80 degrees.

I've been doing some research and posting on forums, and everyone keeps telling me that fin rot and clamped fins are usually due to water quality issues. But I just can't see any problems with the water. I've also read that ick or velvet could be the culprit, but I don't see any white spots, and she's not showing any signs of those diseases - no scratching, no color changes, nothing. She's eating well, active, and always begging for food, except when the lights are out.

I'm stumped - any advice would be appreciated.

[dynamik]

I think you should try doing a water change and make sure you've got a heater in there. Doing a 25% water change might help, and get rid of any leftover food that's floating around, it's just gonna cause more problems if it's not eaten.

[burglar_4]

I'd love to see the tank setup as a whole, could you post a full pic of it?

[musiclover]

I do have a heater in the tank, that's not the issue. I've double-checked the temperature with two different thermometers, and it's consistently at 80 degrees. As for cleaning, I regularly vacuum or use a turkey baster to remove any uneaten food or waste.

[fluxa]

If possible, I'd consider quarantining her to prevent any potential infection from spreading to your other fish, assuming you have some. What's your tank's current stock, by the way?

[musiclover]

Thanks for the suggestions. She's a solo occupant in the tank. I did remove all the plastic plants about two months ago, thinking maybe she was getting cut on them. Now it's just smooth aquarium-safe rocks for hiding spots.

[fluxa]

I think daily water changes could help, plus a thorough gravel clean. Keep a close eye on her, see how she responds. I'm gonna tag @coltin, he's got a lot of knowledge on this stuff.