Err..u can try the method "Isolate the fish in another
container, ten put salt into tt water..coz salt can kill
germs.."
I guess mayb the fish is sick already..so is better to separate it
with other fishes..or else i am afraid wait other fish will also
kena the virus..If by tml tt still doesn't not improve..
u can go to the aquarium shop and ask those ppl..there's a yellow
colour kinda of medicine to help the fish de..
PS: if u wanna change water pls dun change the WHOLE TANK..Jus
change a quarter of it will do..