Foodstuffs for ducks: help please

[Qwerty]

Hello! I have been thinking recently about Life Guard, crushed oyster shell, Poultry spice etc. and have been wondering if they are any good for ducks. I have heard they go down well with chickens. This is a first for us, as we have never really used things like this. Can I have some info about them too, I am a bit confused. The ducks are not ill by any means, and are laying TONNES of eggs, I just wonder if they would help them.Thanks!

P.S I would also like to know about parisite powder, if you know about that. much appriciated!