Underwater Sprints

I did a brief 3,500 yards combined with weights today before a busy day. I did 32x25's with 3 up 1 down. The one down was underwater as fast as I could go, I was averaging about 13 seconds. I've been increasing the amount of butterfly I've been doing in practice in hopes of besting my 49.93 in the 100 Fly in a few months. I still have lots of progress to be made on my stroke rhythm as well as underwater kicking endurance.