Werid Freezing Lager After Dry Hoppong

I am fermenting a 5 gal batch of American Pale Lager. I has been in controlled chamber since 2013.02.16. During this time my blow off water has frozen twice as I have been cranking down the temp of largering. Since the I have added rubbing alcohol to the blow off basin.

This past Sunday I decided to dry hop it. When I went to check on it yesterday I noticed my batch has almost frozen over completely. I turned up the temp so that it will thaw.

I am not worried about the beer, more curious why it froze all of a sudden once I added the additional hops. I have not changed the temp for at least three weeks. I would think if it was going to freeze it would have done so before. Any ideas what is going on?

Not an answer but do not use rubbing alcohol in the airlock. Use vodka. I have had the beer and air in a fermenter contract when I lager at freezing. It can pull the airlock contents into the fermenter. Rubbing alcohol should never be ingested. Methanol is a poison that can damage the optic nerve.

My bad. I noticed you are using a blow off basin.