Sick Bala Shark

[alfspace]

Hi everyone, I have a sick Bala shark, 6 days ago a reddish spot appeared in his body just below the
big top fin, it looks like a bite from another fish, but he continues to behave like always so I just wait,
but 2 days ago his behavior change dramatically so I figured out he is very sick, the spot has turned dark and 2 other dark spots appeared near the big top fin, the fish stays quiet in a corner of the tank, his big top fin is no longer straight but somehow bend over and does not move like before.
Any suggestions on what disease it may be or how to heal the fish ??

I have a 15 gallon tank with another 5 fishes on it,
1 radiant shark, 1 red-tail shark, 1 sword-tail fish, 1 platty and 1 golden fish
I change 30% of water every 2 weeks and 90% of water every 2 months
treat the new water with anti-chloride.
Also have a thermostate which keeps the water at 75 degrees.

Thanks for any help.

 

[Calusa]

I'm sorry I can't help with disease identification, but I'd like to express concerns for tank size. Bala sharks get to be about... 13 inches in length...

 

[Amadaca]

I'm sorry I can't help with disease identification, but I'd like to express concerns for tank size. Bala sharks get to be about... 13 inches in length...

I'll echo that. Dude, you need at least a 120cm, or 4ft aquarium, preferably larger, & should be keeping this shark species in small groups. They can reach nearly 40cm, or 15".

Im sure someone will be able to lend you a hand on the infection, but once healed, for the fishes benefit, it may be best to either hand it back to your local store, or to buy a 120-150cm aquarium & get him some kinfolk.