It sounds like some form of a bacterial infection- go ahead and QT him and start out on 1-2 tsp of AQ salt per gallon, dissolved, 100% daily water changes and see if that helps him out.. if by the 6th day and no improvement, up it to 2-3 tsp per gallon and let us know.. we may have to move to medication if there is no improvement by the 10th day.
Hope it helps him.. I know you care about him, and you are giving them good care.
From my knowledge, the cloudiness could be anything from flukes, to a drop suddenly in pH, to bacteria and fungal... so I'm recommending the AQ salt as that can cover a good range of eye problems, and if it continues then let us know and we can take the next step, if needed. The popping up overnight doesn't point to cataracts.. lets just hope the salt is enough to get him back to normal.
There a way you can get a picture of him?