Brewer's yeast, or other niacin supplements, can take several days to weeks to really help out. If it is a nutritional problem it could take a while to fully work itself out.
Is he holding his head and wings normally? Do you think there may be poisoning possible? If that were the case, then a teaspoon of food grade activated charcoal in the water may help.
I would keep giving a lukewarm bath - no soap, just let him float for as long as you can, half an hour, or an hour, twice a day if possible to get the weight off those legs.
It is always possible the duck has an infection, but without a vet's help it is hard to say.
Please keep us posted on how he's doing.
Is he holding his head and wings normally? Do you think there may be poisoning possible? If that were the case, then a teaspoon of food grade activated charcoal in the water may help.
I would keep giving a lukewarm bath - no soap, just let him float for as long as you can, half an hour, or an hour, twice a day if possible to get the weight off those legs.
It is always possible the duck has an infection, but without a vet's help it is hard to say.
Please keep us posted on how he's doing.