help... fin rot? picked on? bad water?

[Łøäçh_Łøvêŕ]

can anyone help me???
i had a 11 inches clown knife.
i put him into the community tank a few days ago
and a morning i saw the 12 inches hampala barb is nipping his fin and biting his body
the clown knife wasn't moving and sitting at the botton of the tank
then i removed the clown knife and keep him in a single tank
and he doesn't eat since i removed him from community tank
now his fin getting white and im still a newbie
i wanna save him...
but i dont know what to do.....

 

[kno4te]

Hard to make out in the pics. Clean water and make sure it’s eating for now.

 

[Fishman Dave]

If his fins were bitten then it is likely to be a fungal infection rather than bacterial one although both are possibilities. Treatments would include malachite green type or methelyne blue both which can be found in off the shelf medication.
As mentioned, good clean water is essential although you can still make the temporary accommodation acceptable by providing somewhere to hide, as is often their wish when stressed.
Try an earth worm for food or something similar which a) will not pollute the water and b) can be easily removed if not eaten.

 

[Łøäçh_Łøvêŕ]

Hard to make out in the pics. Clean water and make sure it’s eating for now.

thanks dude.now he was healed
but still bullied by hampala.... now is keeping him solo in the tank