Originally Posted by callistra
That's either parasites or he's shedding his slime coat because their is something very wrong with the water. It doesn't sound like either a fungal infection or a bacterial infection to me.
If you could fill this out it would be helpful: http://www.bettafish.com/showthread.php?t=49233
But in the meantime make sure you're using dechlorinator in the water like Prime and pick up some Aquarium salt. You're also probably going to need to be able to control the heat in the tank with an adjustable heater if this is parasites.
What size is your tank? 2.5 gal
What temperature is your tank? 78.0 F
Does your tank have a filter? No
Does your tank have an air stone or other type of aeration? No
Is your tank heated? Yes
What tank mates does your betta fish live with? None
What type of food do you feed your betta fish? Aqueon Betta Pellets, one freeze-dried bloodworm once a week.
How often do you feed your betta fish? 4 pellets every day: 2 in the morning, 2 at night.
How often do you perform a water change? Once a week
What percentage of the water do you change when you perform a water change? 100%
What type of additives do you add to the water when you perform a water change? TopFin PH Decrease, Kordon water conditioner, 4 rocks of AQ salt, Kordon Ammonia Detoxifier. I used to use Stress Coat+ and double the dosage without the Kordon water conditioner because my betta had been tail-biting, and I used to use Stress Zyme+. However, I don't use either of them anymore because I feared that my betta had an overactive slime coat. This is the first week that I have stopped using Stress Coat+ and Stress Zyme+ completely.
Have you tested your water? If so, what are the following parameters?
Ammonia: Not sure the exact number, but it was much too high, so I started using an ammonia detoxifier. I used a test kit with liquid drops.
Symptoms and Treatment
How has your betta fish's appearance changed? Long, white, wispy strands hanging off the tail and fins.
How has your betta fish's behavior changed? Clamped fins (rarely, but often enough for it to be a concern), more aggressive, darting into aquarium decorations.
When did you start noticing the symptoms? 3-4 days ago.
Have you started treating your fish? If so, how? Yes, I put Mardel Maracyn-Two in his tank, beginning the treatment today. However, I did so blindly; I was scared that he had Cotton Wool Disease, so I took precautionary measures.
Does your fish have any history of being ill? Yes, he has had fin rot twice already and has been a victim of a nasty tail-biting habit.
How old is your fish (approximately)? Not too sure, but I bought him from PetSmart and have had him for about 4-5 months.