so I recently went out and baught 12 chickens and 4 ducks..... chickens are a mixture of Rhode Island red, aurucana, red pullets, and Plymouth rock. the ducks are pekin. I've had all of them for about 4 weeks now.. about one week ago I came home from work and one of the ducks was on its side and acted like it was dying.. I picked it up, put it in a bath and made sure its beak was cleared out, let it swim around for about 20 minutes... it acted fine so I put it back and within 2 hours it started happening again. this time it died.... I read that the chick starter feed could be low on niacin so I got a bird multivitamin, probiotic, electrolyte and started putting some apple cider vinegar in there water. now last night the same thing happened to another one. the chicks all act fine and I'm worried the other two ducks are next. I change their water twice a day, change their bedding daily and even give them tons of supervised time outside in the yard. what could be going on?