We have 16 chicks. Seven of them came from a feed store. Two of the 7 keep getting pasty butt. Those two are also really bony. I use a heat lamp, but based off of their body language, they're not overheating. We bought grit, but then noticed that it said not to use it until they're 2 weeks of age. They're on medicated chick starter (Purina). All of the others seem to be thriving. I'm worried about them. I was going to get probiotics and electrolytes from the water, but do you have any other suggestions on why they're so bony?