The orientation of the cinder block Barry uses to keep himself underwater while rescuing Maddy changes. When he first goes in the water it is horizontal (with him holding both ends). When he gets to the bottom of the pool he is holding it vertically (holding only one end). And when he gets to Maddy it is horizontal again (holding both ends).
Big Dave is shown pouring what is supposed to be liquid chlorine into the water circulation system, and then igniting it with his marijuana cigarette. First, the chlorine used in pools and water parks comes in solid form (pellets or discs). And second, chlorine gas is not flammable.