There are three files available:
1. Breath Capacity Decreased (+50% faster breath drain, bigger chance to drown if you not resurface in time, Killer Whale Potion becomes more useful because with it the breath duration becomes approximately the same as in vanilla which is long enough)
2. Breath Capacity Increased (doubles the normal duration)
3. Breath Capacity Infinite (this one's clear)
You can change the drain modifier by changing the value (in file airDrain and airDrainDiving) at the line commented with modAirCapacity.
1. Breath Capacity Decreased (+50% faster breath drain, bigger chance to drown if you not resurface in time, Killer Whale Potion becomes more useful because with it the breath duration becomes approximately the same as in vanilla which is long enough)
2. Breath Capacity Increased (doubles the normal duration)
3. Breath Capacity Infinite (this one's clear)
You can change the drain modifier by changing the value (in file airDrain and airDrainDiving) at the line commented with modAirCapacity.