I have several chicks that are a month old today (hatched June 11). I had 15 healthy, happy chicks that I had been takingoutside periodically, always confined within a pen in my dogs' fenced yard. Late last week, I moved their pen into the garden (which the rest of the flock has access to only in the winter and occasional break-ins). I also moved a pair of older chicks into the same pen, which everyone accepted happily (this is a 10-week-old blind pullet and her 9-week-old helper Silkie). The older chicks are housed in a brooder next to, but separate from, the younger chicks and had outdoor excursions at the same time and place from the younger chicks, but were never penned together until last weekend. While the chicks were outside, I cleaned the brooders and food/water dishes thoroughly and allowed them to air dry. They had plenty of water access, food, and weeds to nibble on. A few days ago, I came home from work to find four of the younger chicks dead in the brooder. None had shown obvious symptoms, but may have been a little less active the night before. I was concerned about fighting, but the next night, I saw bloody diarrhea. Another dead chick the next morning, so I picked up some Corid as soon as the store opened. I began treating the younger chicks and saw an immediate improvement. Neither the older chicks in the next brooder, nor the outdoor flock, have shown any sign of problems, but I assume I should treat them as well. That's no problem with the older indoor chicks, but the outside flock will be more difficult. My outdoor flock consists of 5 ducks (1 broody with eggs due to hatch any time), 12 adult chickens, 3 ten-week-old chicks (siblings of the blind chick), and 4 six-week-old chicks. They free-range in a fenced portion of my yard and I have no way to separate the ducks from the chickens. Their water sources are a 5 gallon dish that the ducks spill quickly and two wading pools. If I take away the pools, I can dose them in the dish, but the ducks will waste a lot of water. Also, is it safe to give ducks Corid? Do I use the same dosage (2 tsp per gallon) on the asymptomatic birds as I'm using for the infected chicks? Finally, there are two remaining chicks from the younger indoor bunch that I intend to keep and will introduce to the flock when they're around 10 weeks. Should I be concerned about re-infection at that point? What about on future trips outside? Will the flock get re-infected just from being on the same ground?