This was more like 140 for a couple of hours, then 200 for another couple of hours. Same result though
I read that if you do it more slowly you get fewer white bits on the surface, it seems to be working. It takes a while, but it's great!
I wouldn't care so much if this was just for me and the family, but I'm trying to get a really nice looking whole filet for a party in a couple of weeks.