Help me please!!!

I have had an accident with a newt, as I was putting rubbish in the outside bin, to my horror I trod on a newt, a considerable ammount of pressure was put on him before I realised it feld squashy as I took my foot (rather quickly) off, it skweaked, to my suprise when I attempted to move it it seemed alive and well. I have just put the newt into my fishtank, its a cold water one, and contains two twin tailed goldfish. I wanted to monitor it for a few days before releasing it, I have compaired its picture to a few off of the internet and it looks like a palmate. Can anyone please offer me advice on how to care for it as best I can for its stay in the tank? I would like to know whats best to feed it, how to check if it has any injuries since its encounter with my foot, and whether or not I can turn my water filter back on? Thanks. Tommy,