Sodium Hypochlorite is a liquid Chlorine and has around 10-12% available Chlorine. Available Chlorine (AC) is the amount of Chlorine released in the water to disinfect. Bleach, which contains Sodium Hypo, only has 5% AC which is why bleach is not a good pool disinfectant. Because of its liquid nature Sodium Hypo is usually applied to a pool through an automatic chemical feeder. Big water parks and large commercial pools are the common users of Sodium Hypochlorite.
Side note: Salt pools are still Chlorine pool because the salt cell breaks the salt down into Sodium Hypochlorite.
picture is for displaly only drums may vary in colour shape ect