I got to 70 but I think if I practiced I could get 80. Very cool. I've never really held my breath for that long, and it puts you in a really relaxed state. I like the way the music fades out as you go deeper and fades in as you approach the surface. When you hear the music again, you know you can make it without dying.
I must say, I quite like the simplicity of the one-bit aesthetic as it stands; I think you did a good job and it pairs well with the relaxing piano music. Though I play with my eyes closed because I find it makes it easier, haha. I've cleared 90m and I'm going to keep trying every now and then until I can beat the game.