If it's Actually frozen, don't put it in your tank it's just going to rot
But if it's just cold I would try it, watching closely for a couple of days - the moment it starts to disintegrate chuck it
I'm south of St. Paul and happy to report that my cold Chaeto warmed up and seems fine. Did you have a favorite fish store in this area? I'm new to sw (3 months) and still learning.
-Beth
I think as long as it is still green it will be OK. Just tear off any that is white , brown or soft and chuck it.............Fast water flow and some light is about all it needs.....