I am very sorry you lost one of the little ones. I want you to know that there was nothing you could have done differently to have a different outcome. I have had a few years of relatively good luck with very few chick losses. This year I have more then paid up for it. It is a hard pill for me to swallow that no matter how hard you try you are going to loose some. If you have a weak chick the best thing you can do is keep it warm, offer nutridrench, save-a-chick or even sugar water to it. If all it needs is that little boost it will do the trick. If it does not know that nothing you try will have prevented the outcome, instead you ended up prolonging it. The one this year that took me by surprise was the silkie, and the final straw where I just need a break from chicks. It acted totally fine. It was active, it ate, drank and pooped. It appeared to be growing, but it was tiny just being a silkie. If I had any warning that something was off it was that last night and I chalked it up to nothing. When I moved it and Perdita to their nest that night and it got under her it did  not immediately quiet down. It peeped, but not loudly or like it was in distress for a few minutes. I actually did not leave until it stopped. The next morning it was gone. No sign of truama, it literally looked like it was passed out sleeping. Poor Perdita looked and called for her chick for 5 days and chased me around the house thinking I had it a few times. Deep down I know this will not happen with every hatch and things will get better, but right now it still hurts.