Our chick (squishy) had pasty butt once we soaked her and then picked off the poo. She got this a few more times but as she grew the problem disappeared. If they have long feathers on their rears then I would suggest clipping them down around that area. Good luck to everyone who still get this...
Our roosters had mites really bad. We used sevens powder to get them off at least. He recovered luckily. This might not help your roo but you can prevent it with sevens next time. Good luck!