OK so I have a giant female plakat betta fish, about 9 mos. old, with holes in her fins. She's in a 10 gal tank with filter. Change carbon every month. Water parameters have been consistent throughout the time I've had her:
Ammonia 0 (30% water change once a week)
Alkalinity in "ideal" range between the 120 and the 180 colors
chlorine 0 - I leave her water out in the same room with her for at least 24 hours before water change to let the chlorine evaporate and the temp reach the same temp as the water in the room
I put 1/2 tsp of aquarium salt in for each gallon during every water change.
I had not been using a heater, because I got her in June, and its not super cold here yet. My house is a consistent 74-75 degrees. Her water temp during the fall has been 72-74. I am wondering if that is too cold for a betta? I've since put a heater in her tank, at 76-78 degrees. She is very active, happy, hungry, eating well, etc. doesn't seem to notice her fins. One thing is, during the hurricane last month we lost power for 3 days and her water temp dropped to 70-72 degrees, I checked it constantly and during the nights I put hot water treated with Prime in to bring the temp up a degree or two until the next day when it got warmer. Nothing drastic just a degree or two. After the power came back on, I threw out all her old filter media and replaced it, and since I wanted to be extra careful I did the 30% water changes every 5 days instead of every 7 and kept an eye on the water parameters to make sure everything was ok while the biological filter in her filter media re established itself. Everything has been perfect. So 4 weeks after the power outage was when she started to get holes in her fins. Is it because her water temp dropped too low during those 3 days? Can fin rot take 4 weeks to start actually causing holes in the fins? Or is it because 72-74 is too cold for her? I have 5 other bettas in other tanks and they all seem to do fine at that temp.. is that too low?
Thanks for everyone's help!