The older I get the more I realise that life is about finding the easiest way to do things and scuba diving is no exception. Doing everything in slow motion will stretch your air supply. You ought to kick your fins, move your arms and turn your head as though any motion were almost too exhausting to attempt because it is. Water is 800 times denser than air so moving an arm or leg in water requires a lot more energy than it does in air. Energy is fuel plus oxygen, so the faster you burn energy the faster you empty your cylinder. It’s that simple.
Slowing down conserves energy and air because speed is very expensive. For those who’ve forgotten physics class, the energy cost is proportional not just to the speed but to the square of the speed. Swimming twice as fast requires four times the energy. Swimming three times as fast requires nine times as much. And the converse is true too: if you cut your speed in half, you need to burn only one-fourth as much energy and one-fourth as much air.
It takes a conscious effort to move at Tai Chi speed, but practice will make it second nature. The payoff is bragging rights over your air-hog buddy at the end of the dive.