If you have quite a bit of grower left start mixing it into the feed for them all and just put out Oyster shell for your layers. since your ducks are 19weeks old your female needs an extra boost of Oyster shell since she is getting close to laying. . Put it close to where their feed is and the layers will eat it as needed. It won't hurt the rest of your birds to eat the grower mixed in.I'm new to keeping ducks and iv read all I can and spoke to people but I'm still confused on what to feed my ducks I have 2 aylesbury ducks 1 duck and 1 drake they are kept with chickens and they all share feed so I now buy a feed that they can all eat but my ducks are about 19 weeks old and iv kept them on grower pellets my girl ain't laying yet is it ok for them to still be on growers or should I be feeding them something else?