Sick silver shark

[mickrabb]

Hi guys,

I have three silver sharks and the last couple of days I have noticed what looks like blood on one of their fins and gills. My water chemistry is within it's limits and i do regular water changes. Is this some kind of bacterial infection? If so is it contagious and how do I help my shark to get better?
I haven't added fish to my aquarium in a over a month so I don't know how this has happened.

Any help would be great

 

[Delapool]

Yes, could be - I'd try increasing pwc's for a bit.