For worming I just give all birds flubenvet, I just get pheasant meal with it already mixed in. It's a lot easier when the birds are free ranging rather than in the water.
I did have a duck that lived with hens and seemed happy, it didn't like ducks. At least she has company in your chickens.
I saw someone was looking for the dosage for denagard for chickens, I googled it and just thought I'd post it.
denagard 12.5%
Chickens: The dosage for chickens is 25 mg of active substance per kg bodyweight (equivalent to 100 ml of product per 500 kg bodyweight). Tiamulin should be administered...