I got this off the internet... U can see it that seems like your problem...
DISEASE: VELVET
uGENERAL INFO:
Velvet is another pesky little parasite. If you always add aquarium salt to your betta’s water (1 teaspoon of aquarium salt per 2 1/2
Gal of water) and one drop of Aquarisol per
gal, your betta will probably never get velvet. It is very contagious, but bettas will fully recover if treated promptly. Velvet is the number one killer of small betta fries.

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uSYMPTOMS:
Velvet is hard to spot, but can be best spotted with a flashlight. Shine the light on the betta’s body: if it looks like it is covered with a fine gold or rust mist, then it has velvet. A betta with velvet will act sick, so look for clamped fins, scratching against rocks/gravel/tank, loss of appetite, loss of color etc...
uTREATMENT: Velvet is a parasite. Because velvet is very VERY contagious, it is preferable to treat the whole tank when one fish is found to have it. BettaZing (included in our Betta First Aid Kit) contains two agents that are proven velvet killers, so it is EXTREMELY effective against this disease

. So far it is the meanest velvet killer I have ever found

. Use Bettazing at a 12 drop per gallon concentration (yes, it is OK to do so you have my blessings). Isolate any individual with velvet, treat the whole tank even if other fish look OK and remember WASH YOUR HANDS!!! Sanitize fish nets! Keep bowl or tank in a darker place, velvet will be easier to kill if it is not getting any light.