I've never had trouble with coconut coir. Also, my Russian definitely reacts to the winter light cycle and spends most of his day sleeping. I do wake him up and make sure he eats and soaks.
I would first double check your temps before worrying about the coir.
I've been away from home for two weeks. My torts have been under the care of my husband and children so I know that neither their temps nor diet changed when I was away.
When I soaked my yearling sully this afternoon he peed a huge amount of orange liquid. He hasn't eaten anything orange...
No wonder he always looks like he's smiling.
Love all the tort tables. There needs to be an archive with table building blue prints so I can steal them.