your friend hated him, strong words for a harmless little frog, oh well at least he can get looked after properly now. My advice is treat him like a fish, maybe do a full water change if it's that bad, but I'd probably more go along the lines of 75% first time and 25% every day until it's clear. Like megthefish says we do need some more info, like size of tank, filter, etc. and how green is the tank, (can you see the frog?)