drake not eating

[Drachma]

So I noticed yesterday that my khaki drake is a bit off. I was digging in the compost pile to add to my garden beds and usually my ducks are right there 'helping' but the drake just hung back.
He was still acting normally otherwise drinking and pushing the girls around so I didn't worry too much.
This morning he didn't eat before going out and didn't hop in the pool with his girls and when offered banana (his favorite) he got excited and ran for it, but didn't eat any.
Any thoughts or suggestions?

 

[Whittni]

Sour crop? Has he been wormed in the last 3 months?

 

[Drachma]

He's only about 4 months old. I've never dewormed him. I'm new to duck keeping, so please forgive my ignorance, but should ducks be dewormed regularly? And what are the recommended dewormers and dosages?
Boy! I hope its nothing like paste deworming my pony! Lol
By the way, I did dose him with electrolytes and his appetite did pick up a bit, so he seems to be doing better.

 

[Blackberry Hill]

Hi --- How long have you had him? And he is normal except his appetite is down? What do you feed your ducks EXACTLY?

Do the ducks go grubbing for earthworms in the compost etc?

It could be parasites. I am just trying to cover the bases and rule out illness.