As you descend, water pressure pushes on your eardrums. Equalising adds air to the middle ear to balance it.
How
- Equalise at the surface, then every metre on the way down — before you feel pressure, not after
- Pinch your nose and gently blow (Valsalva), or swallow/wiggle your jaw (Frenzel)
- Descend feet-first and slowly; stop and ascend slightly if it won't clear
Never force it or keep descending through pain — that risks a barotrauma. Don't dive with a heavy cold.