well thanks all for the replies. The tank has got some live plants in it. the Tank is 240litres and has bn cycled, i upgraded 2 it in Jan. The bala shark was only an inch and a half at this time, his tank mates consisted of a common pleco 5inches big, 5 minnows, 3 danios, 3 rosy barbs, 3 bronze cory's,2 peppered cory's and a weather loach.
I took him out a couple of days ago and put him in my hospital tank on his own, all other fish are fine and doing really good. Sadly my bala shark passed away late last night.