Seriously! If that is your community tank stocking in your signature then you will be looking at aggression in your tank very soon, i'll get on to the betta in a sec, but to drill my point, have a look at this vid;
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Black ghost knife feeding time or if the linking is playing up use this address;
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/www.youtube.com/watch?v=QnUhy2FiSC4
You see those big, fish sized chunks of meat he is eating? Thats why he's not community suitable!
How big is your tank, they look cute when you buy them, but get HUGE.
The betta splendens, you may be aware of the common name; siamese fighting fish...
This says it all, they are not community fish, while lovely and fairly suitable with smaller unrelated fish it comes from the group known as 'anabantoids' the same as gourami, they will more than likely fight eventually, and more than likely; to the death.
Betta should not be kept with other anabantoids.
They also shouldn't be kept with nippy fish, when fish see something floating past them they often assume it is food and bite at it, if your betta sufferes more stress in this manner then in my opinion he won't last long, ill or not.
In addition, if it is an illness rather than a settling in issue there is also the possibility he may contaminate your other fish.
You need to take this on board, nobodys lecturing you, they are only trying to help you out and prevent you suffering any losses or difficulties.