Salt water vs fresh water buoyancy

Salt water provides more lift than fresh water. This happens because salt increases the density of the liquid. You will feel lighter in the ocean than in a pool.

Most divers notice this when moving from a lake to the sea. Salt water density is roughly 1025 kg/m³ while fresh water is 1000 kg/m³. This difference means you need less weight to stay neutral. If you use your pool weights in the ocean, you will float too high.

Buoyancy shifts change your trim. Always check your buoyancy in the first 5 m of a dive because your wetsuit compresses as you descend. I once lost 1.5 kg of lead weight in Koh Tao because I used my freshwater training weights. This mistake made me struggle to stay down at 18 m. Always re-check your weight belt before you leave the boat.