I would clean most of attached algae from cages before ice formation. I try to have my cages free of algae growth before the fish have to endure the rigors of winter. If the algae on cages is a cold water algae it could get a little more growth under the ice or after ice melt. Cold water algae growth could easily increase on cages since I try to keep the snow off ice around the cages which allows light penetration around the cages. A little algae on the cages could help keep DO slightly higher around cages.
