As K says, does he move at all when you touch him? If s/he does look like its still alive then put him in container in the fridge, with water low enuf for his feet to touch ground. Two of our leuc axies went completely white a few months ago, one skitzed out and other slightly lopsided swimming and we put them both in the fridge for two weeks; giving them complete daily water changes. Not sure what was wrong as our other leucs weren't effected. After two weeks we took them out of fridge and kept them in same containers, with daily water changes, to monitor and feed them. Was about 5 weeks b4 they came right and were returned to their tank.