Hi all, this will be my red-eared slider's 1st winter in her new pond (after living in an indoor tank previously). I took advice I found in prior threads and placed a litter pan filled with sand on the pond floor. The pan has been there for about a month. The past few nights have been in the 30's and the turtle has yet to use the pan. She tucks inside her shell in the fish cave. It will be in the 20's in a couple days. Should I be concerned?