How to relieve ear pressure when at bottom of 12ft deep pool?

plug your nose and exhale gently as you go down. it equalizes the pressure in your sinuses. to get the pressure to alleviate, i find that it helps to swallow a few times as i'm coming up. just don't swallow any water, that's gross. also, to minimize pressure as you go down, go down feet first as far as possible before you turn over to grab the brick.