They do grow really quickly .... that's norm as they are fully grown and mature by 6/8 wks.
You don't think it could be anything to do with the wood chippings

. We have always reared ours on shavings. They do seem to roll and topple about more than chicks in the first few days but usually very strong by 3 wks.
You could try medicated crumbs but doesn't sound like symptoms for cocc.
Think if it were me I'd just try shavings.