Is it 5 week from cut, or 5 week from initial rooting?
They don't look THAT far behind and they have some nice
thick root structure developing, but there does look to be a
slight browning going on to some of the roots. What are your
reservoir temps at? Many people complain about those fog
units heating up their reservoir way too much and if it's the
earlier stages of root rot that could explain your slowing growth.
Just a theory still need more details