Build Your Own Water Filter for Your Fishtank

Yesterday saw the death of one of my fish. Sanctam went off his food and lost all his colour. I took him out of the fish tank in case it was too warm or cold for him and put him in a separate jar. There, he copped it and when I went to look at him this morning he was floating around dead. The others seem happy enough, so I don't know what happened to him. Sad. Still, I just found this on youtube on how to make your own water filter. Fascinating stuff!