The moss problem is an old one with CP and make it rough on seedlings.
You might try trimming the moss back with scissors, and transplant the
seedlings to fresh media when they are large enough. My judge of
transplant maturity is when I can (with reasonable care) manipulate the
plant. Usually it has 5-6 real leaves and around 5 mm in dimension.
You will probably never get rid of the moss totally as the spores are
air-borne and come in on the breeze. It does make an attractive top
dressing for larger plants though.
Good Luck!
Jeff