how was he cared for at babysitters, ie.. tubbed, tanked etc..
ensure water is cold (around 15°c), and oxygenated, give daily methyline blue baths as well as adding 3.5g/l non-iodised salt to any water he is in, try feeding him small sized food ie.. bloodworm, brine shrimp etc.. not too much though, can be fed multiple times per day until he has put on mass.