I have a fin question about brown fuzz on pectoral fins (when I goggle search, the results are always related to white fuzz). My female crowntail betta has fuzzy brown "pieces" that seem stuck in her pectoral fins, which haven't gotten worse or better over the past couple of months. She is a dark blue fish with reddish shades on her outer fins. The fuzz hasn't impeded her use of the fins. She doesn't appear to have any other ailments --- eats hungrily twice a day, swims and takes breaths normally, wiggles, etc. I'm hesitant to start adding medicines as I don't know what the issue is. I've had her for about 6 months and this appeared a couple of months ago, but I haven't been able to find an answer to this issue and her activity/behavior has remained normal.
She lives in a 5.5g heated, filtered, lit, planted tank with an airstone that I turn on for about half of the day (it's noisy, so I turn it off in the evenings). I do 25% water changes every week with a dose of betta water conditioner added.
Is this a fungus? How to rid it without killing the biofiltration in the tank?
Thanks for any advice!